The heart of the reptilian conspiracy idea is that there are, today, reptilian humanoids living among us (as in the TV show V) who have infiltrated human society for nefarious purposes. Most conspiracy theorists say that the reptilians can shape-shift between human and reptilian forms (though in some versions of the conspiracy, there is one tier of "pure" reptilians who cannot shape-shift, and another tier of human-reptilian hybrids who can). According to the conspiracy theory, there are certain bloodlines descended from reptilians which continue to be in positions of power, allowing reptilians to subjugate us to their will. Most world leaders are said to be reptilians. There is also a popular past-time of posting Youtube videos identifying transforming reptilians - most of which are simply videos of people who start to lookscaly due to compression artifacts ( web site which explains various JPEG compression artifacts).
The History of the Reptilians
As is the case with a lot of UFO mythology, there are many variations on the general "reptilian conspiracy" theme. Some people seem to beleive that the reptilians cameform another planet (as Credo Mutwa seems to insinuate in the David Icke documentary "The Reptilian Agenda"), while others believe that the reptilians originated on Earth and simply live underground. For anything specific that I say here, there is probably some conspiracy theorist who doesn't believe it and has an alternate history of the reptilians. That said, none of these details seems absolutely critical to the nature of the reptilians, so it's probably best not to get bogged down in arguing about the details.
The big proponents of the reptilian conspiracy that I have found are a guy named John Rhodes and the popular "conspiracy researcher" David Icke. In both the Rhodes and Icke formulation of the reptilian history, at some point in the distant past, reptilians openly walked among humans and ruled them as gods, using their superior "spiritual powers" and technology. The reptiliansbred humans for some nefarious purpose - presumably forced laborers, and used them to work in the fields. This time of coexistence is said to have been the reason for the similarities in many world religions. There is a long document by John Rhodes called "The Reptilian-Human Connection" which details some of this backstory wherein he purports that the Sumerian gods were genetically engineering humans for their purposes and that one "fallen god" named Ea engineered us to understand what was going on allowing us to break free from the rule of the reptilians. This Sumerian connection seems widespread in the reptilian conspiracy, as the reptilians are often called the "Annunaki", who were Babylonian deities (though I believe that there is some sort of feeling that the Annunaki became the Nephilim of the Bible, who are also purported to be Reptilians - but this mixes in with other non-reptilian New World Order human subjugation conspiracies as well). Other gods identified as the reptilians are Quetzacoatl, the meso-american feathered serpent god, the Naga, who are snake-deities from northern Indian religions and Satan, who took the form of a serpent when offering Eve the apple of truth (as well as many others). David Icke also has a ridiculously long documentary called The Reptilian Agenda, in which he interviews a Zulu shaman named Credo Mutwa about his beliefs about the reptilians - which he calls the Chitauri. Mutwa purports that these reptilian gods are part of Zulu mythology, and goes into detail about how belief in ruling reptiles has been a part of the secret history of the Zulu since ancient times. It is not clear to me if this is in line with mainstream Zulu beliefs or not.
Icke and Rhodes differ on their conceptions of the origins of the reptilians. Icke believes that the Reptilians originate from another star system known as Alpha Draconis, while Rhodes believes that Reptilians evolved from dinosaurs on Earth before humans came around, and so their home planet is Earth. Both men believe that the reptilians can use interstellar flight and currently live in an underground network of caves on Earth as well as off-world and in "alternate vibrational states of reality". At least Rhodes purports that the commonly seen (in UFO mythology) "grey aliens" are in fact another genetically engineered race created by the reptilians as servants in their underground caves.
David Icke is a sort of uber-conspiracy theorist (as many of these people are). While he is often known because of his belief in reptilian control, the reptilians conspiracy is actually a part of a wider new world order conspiracy which includes almost all other conspiracies. His core belief seems to be that there is some shadowy group of people controlling humanity (alternately called the Satanists, Reptilians, Annunaki, Chitauri, Illuminati, etc) whose core goal is to prevent us from reaching our full potential and to maximize our suffering. He believes that humans (and reptilians) are "higher-dimensional beings", but that the Reptilians suppress our ability to perceive the universe in a number of ways. He cites fluoridation int he water supply, HAARP, chemtrails, genetic engineering, vaccines (and probably a number of other conspiracies that I haven't heard him mention). The reptilians do this so that they can induce suffering in us, which produces negative emotional energy, off of which they can feed. To do this, they have infiltrated all levels of government and use this to create conflicts and wars. There's also an elitist "bloodlines" element, as he often cites that all of the world's leaders tend to come from the same bloodlines - which he believes are bloodlines descended from the reptilians. He is quite articulate and extremely prolific, and as such he has gained a fairly large audience of followers.
Lizards... or Jews?
It has often been suggested that the reptilian conspiracy is actually a euphemism for a Jewish conspiracy. That is to say that when David Icke says, "The lizards control the world", he means that the Jews control the world. When asked about it, Icke insists that these sort of efforts to read antisemitism into his "conspiracy research" are merely attempts to discredit him. In his BBC Documentary Series "Secret Rulers of the World", Jon Ronson addresses this issue in the episode "David Icke, The Lizards and the Jews". I get the impression that to Icke, Jewish conspiracies are a subset of wider New World Order conspiracies, and that the Reptilians have infiltrated the Jewishhierarchy as well as the Catholic and Islamic hierarchies. This seems consistent with his wider system of beliefs, as his rhetoric focuses less on anti-Reptilian sentiment and more on taking control back from the nameless, faceless entities which currently control all aspects of the universe.
Origin of Reptilian Beliefs
The evidence for a reptilian conspiracy is, at best, largely based on anecdotes and pattern-seeking in "ancient texts" - as far as I can tell, most "conspiracy researchers" hear about the idea of reptilians, then go looking for evidence to support the hypothesis, rather than independently coming to the conclusion that human-reptile hybrids rule the world. As such, it would be interesting to know from whence the belief originated. Unfortunately, there is not a very clear line about where the conspiracy originated. The best source for this that I've found is this David Icke Forum Thread, in which user efan attempts to track down the first mentions of the reptilian conspiracy. The earliest reference he finds is to a 1934 Los Angeles Times article "Lizard People Catacomb City", followed by a burst of activity in the late-80s/early-90s which seems to be initiated by conspiracies about the New Mexico Dulce base. Brian Dunning analyzes these claims in his Skeptoid episode on the subject. he article describes a geophysicist named G. Warren Shufelt, who heard about an Indian "Legend of the Lizard People", in which advanced Lizard People dug a series of catacombs under Los Angeles using advanced chemical technology. Believing he would find their treasures, he used a "radio X-ray device" to map out a series of catacombs below the surface, and then dug a 250'/76m mine shaft to attempt to access them (which immediately filled with water). Dunning does not find the "Legend of the Lizard People" credible, as his research turns up no such record. In any case, this Catacomb City has very few similar elements to the current Reptilian mythos, and if anything it seems like the origin of the modern reptilian conspiracy comes out of UFOlogy and Dulce Base conspiracies.
Dulce Base is a "secret" underground base in New Mexico, allegedly created under the cover of underground nuclear testing. According to John Rhodes, it is laid out as large central caverns with hallways branching out, resembling a "Hopi Kiva". In Dulce base, Reptilians and greys run horrifying genetic experiments on humans for nefarious purposes.
Unfortunately, with regards to the reptilian conspiracy, there aren't a great number of factual claims to assess. In general, reptilians are another of the shadowy branches of evil forces out to get us which constitute "Them", but their existence is considered so absurd that most people either believe that they exist or don't. Generally, evidence for reptilians is given in the form of "someone is controlling us and has been for a long time, here are a bunch of examples of things which might be interpreted as reptile-gods, it must be the case that reptilians are controlling us."
The first part is a problem because it establishes as a premise of the argument that "someone is controlling us" - which is something that appeals to conspiracy theorists, but not those of us who are skeptical of conspiracies. This comes out of the general theme of needing a source of agency in distributed processes, as far as I can tell (the same thing is seen in claims about evolution, where it seems "obvious" to some that there must be some sort of agency involved in creating species).
There are a number of problems with the second part of the argument, which takes as a premise that powerful reptilians exist in many mythologies and concludes that this reflects an actual worldwide status quo during the emergence of these mythologies. While this is one explanation, it is hardly a unique conclusion from the facts. Taking as true that all cultures have a form of "reptilian" beings in their mythology, there are a number of explanations for the phenomenon. For example, it is possible that all cultures descend from a common culture whose mythology included fictional reptilian beings. Another possibility that is more likely than it seems is that multiple cultures independently came up with a "reptilian" metaphor for powerful beings. People tend to be suspicious of stories about independent developments of similar concepts because these concepts are considered almost as being drawn at random from the space of all stories one might tell - sort of like if humans randomly pointed at words in a dictionary it seems phenomenally unlikely that any two people would ever come up with the same 1000-words in a row. However, the creative space is actually much more restrictive given that humans all have the same sort of brain and are all likely to lead similar sorts of lives. There are snakes and reptiles everywhere on Earth and humans think enough alike that it is not at all unreasonable that they would anthropomorphize reptiles in some way.
Additionally, there's also the strong possibility of confirmation bias here. If they were so inclined, one could almost certainly find similar examples of cross-cultural shared mythology that have nothing to do with reptiles. I imagine you would be able to build a similar case for any kind of variation on common human themes - humans with too many arms or too few, humans who are too tall or too short or with weird proportions, or other forms of animal-human hybrid (people with wings, people with animal heads, etc). It all depends on what you start out looking for.
Finally, going back to the beginning of the second claim, it is also in no way obvious to claim that all cultures have forms of "reptilian" beings in their mythology - at least not in the sense that I see. Where there are reptilian beings, they often do not have anything near the same form. For example,Queztacoatl and the Naga are both legitimately serpentine creatures, but Quetzacoatl is a sort of flying snake, while the Naga are more like people with a snake body where their feet should be. Neither of these are consistent with reptilian humanoids. Additionally, while the Nephilim and the Annunaki are taken as evidence for reptilian presence in mythology, it does not seem to me that they are actually described in their original texts as reptiles, but rather they are god-like beings who happen to fit a certain narrative which is seen as consistent with the reptilian story. It seems to me that it's a bit like writing a story where Hercules fights Darth Vader in the dreamtime and saying that there is a convergence between Greek mythology, American storytelling and Australian aboriginal religion.
The other main evidence put forth for reptilian conspiracies is this argument from bloodlines, which is that rich and powerful people tend to all be related in some way, and that there are certain "bloodlines" which are kept in the ruling class. This is basically overlaying a reptilian framework onto common "secret society"/"New World Order conspiracy theories. There are likely people who believe that there are favored bloodlines who do not believe in a reptilian theory, but the aspect of Reptilian genetic engineering fits in well with the idea of hybrid bloodlines. Again, the same sorts of lines of reasoning can be used to evaluate these claims. The first thing to ask is "is it true?" that there are preferred bloodlines. It could easily be true that most world leaders are in clusters of relations going back 50 or 100 generations, but it could also easily be true that the same sort of "clustering" behavior is exhibited by any random selection of people. Consider that the number of ancestors that you have is exponential in the number of generations back you go (assuming no inbreeding). That is that you have 2 parents, 4 grandparents, 8 great-grand-parents, 16 great-great-grandparents, and when you go back 20 generations, you should have over 1 million direct ancestors in that generation alone (in total, you have over 2 million direct ancestors going back 20 generations). There is not a unique set of 1 million people 20 generations ago for each person who exists today, and you expect there to be a large amount of overlap.
The second thing to ask is that even if it is true, does that necessarily imply that there is some deliberate force at work keeping these bloodlines in power or is it a selection effect. So even assuming that the more powerful people do have a greater degree of "ancestral clustering", is that unexpected? One possible selection effect that may be more plausible than reptilian genetic engineering would be historicalcontigency - if you are in power you are likely to consolidate your power by helping out the people you trust, which is more likely to be your family members. Additionally, there's the possibility that if you are rich, your children may be provided more opportunities to become rich themselves. Personally, I think that this is likely to be a smaller effect than the normal ancestral clustering, but a larger effect than reptilian manipulation of bloodlines.
Reptilian Transformation Videos:
The Dulce Book - http://www.thewatcherfiles.com/dulce/chapter1.htm
The Reptilian Agenda with Credo Mutwa (David Icke) - Youtube
User Who Uploaded: http://www.youtube.com/user/iameiamfree#g/u
Part 1.1.1: http://www.youtube.com/watch?v=ctIpUmJjkAs
"The Reptilian-Human Connection" by John Rhodes - http://www.reptoids.com/Vault/ArticleClassics/1994RepHuConn.htm
David Icke's Website - http://www.davidicke.com
Reptoid Research Center (John Rhodes) - http://www.reptoids.com/
Ronson, John, "Secret Rulers of the World: David Icke, The Lizards and the Jews" (Google Video Link: http://video.google.com/videoplay?docid=-2912878405399014351#)
Dunning, Brian, "Support Your Local Reptoid", Skeptoid Podcast, Skeptoid Media, Inc, 21 May 2007. Web 6 Jun 2010
Also, I found some other interesting things you may want to feature in your show when doing the research for this. One is the conspiracy theories surroundingDucle Base, which seem like they go beyond the Reptilian conspiracy (which is why I didn't go into too much detail about them here), and the other is this fascinating story about Dwight York, who was the founder of a cult called Nuwaubianism, which is like a mixture of black power movement and a new age cult. The relationship there is that the Nuwaubians incorporate many New Age beliefs into their crazy shit, including their belief that humans go through a grey alien stage and a reptilian stage during fetal development. He also states that there are 70 species of grey aliens and 16 species of Reptilians on Earth. I didn't really include him in this because 1.) His story is so fucking crazy and complicated that it deserves its own separate topic (he is currently in jail for molesting over 100 children) and 2.) while his Nuwaubianism actually far predates the Dulce Base/David Icke stuff, it's not clear to me that he incorporated the reptilian-conspiracy stuff into his religion before it came into the mainstream, so it wasn't really worth mentioning. I definitely suggest a podcast on Nuwaubianism.