Dave Arneson is officially credited with co-creating the original Dungeons & Dragons game. There's much debate as to how much he created (Gary Gygax seems to take the lion's share of the credit) but it's certainly true role playing would not exist as we know it today if it were not for Arneson.
In the '60s Arneson staged Civil War reenactments in Minneapolis/St. Paul. He belonged to a group called the Midwest Military Simulation Association (MMSA). The MMSA was a counterpart to the Lake Geneva Tactical Studies Association which had Gary Gygax as a member. As a member of the MMSA, Dave Arneson enjoyed playing Napoleonic miniature games. He wrote Napoleonic ship combat rules called Don't Give Up The Ship! It was published by Guidon Games in 1971, which also published Gary Gygax's Chainmail rules. Arneson and Gygax made contact with each other as game authors through Guidon.
While the miniature games were fun, such straight out
games became boring after a while and began to take on more role playing
aspects (e.g., people played individual officers with personal missions).
Arneson participated in a Napoleonic role playingesque game set in
Arneson's Blackmoor campaign was very popular with the
MMSA gamers in the Twin Cities. Soon
Putting their differences behind them, Arneson created a Blackmoor supplement for D&D in the fall of 1975. In the '80s, Arneson formed his own game company called Adventure Games. He returned to producing miniature war games, including the modern naval warfare game Harpoon. Arneson also contributed to some computer games, including the ill fated Bard's Tale IV, which never saw the light of day.
In 2000, Arneson completed work on a documentary called Dragons In The Basement. The documentary is about the genesis of role playing, and includes interviews with Gygax and other early founders. It's uncertain if it's aired (beyond a showing at Gen Con 2000), although Arneson is looking to sell it to PBS or Sci Fi. You can see a preview at his web site.
Arneson generally occupies his time these days lecturing
at role playing conventions and teaching sailing at a private university in
-- Karl Mamer