David Lance Arneson (/ˈɑːrnɪsən/; October 1, 1947 – April 7, 2009) was an American game designer best known for co-developing the first published role-playing game (RPG), Dungeons & Dragons, with Gary Gygax, in the early 1970s. Arneson's fundamental early role-playing game (RPG) genre work pioneered now-archetypical devices, such as: cooperative play to develop a storyline instead of individual competitive play to "win"; and adventuring in dungeon, town, and wilderness settings as presented by a neutral judge who doubles as the voice and consciousness of all characters aside from the player characters.
Arneson discovered wargaming as a teenager in the 1960s, and he began combining these games with the concept of role-playing. He was a University of Minnesota student when he met Gygax at the Gen Con gaming convention in the late 1960s. In 1971, Arneson created the game and fictional world that became Blackmoor, writing his own rules and basing the setting on medieval fantasy elements. Arneson took the game to Gygax as the representative for game publisher Guidon Games, and the pair co-developed a set of rules that became Dungeons & Dragons (D&D). Gygax and Donald Kaye subsequently founded Tactical Studies Rules in 1973, which published Dungeons & Dragons the next year.