Dave Arneson was the co-creator with Gary Gygax (obituary, March 6, 2008) of the fantasy role-playing game Dungeons & Dragons. Their creation attracted hundreds of thousands of players, made a fortune, spawned a genre of fantasy games and had a profound influence on the multibillion-dollar computer gaming industry.

Arneson’s love of role-playing was the impulse that turned Gygax’s blueprint for the war game Chainmail into the archetypal hero adventure, Dungeons & Dragons. Arneson believed that a good story lay at the heart of a good game, and developed many of the fundamental elements of role-playing: that players control a single character, that skill is gained through experience and that personality is as important as strength.

Dave Lance Arneson was born in 1947 in Minnesota. It was through his teenage enthusiasm for table-top war gaming that he met Gygax, at the Gen Con gaming convention in 1969. The event, which then had only a few hundred attendees, now attracts tens of thousands of visitors a year.

The pair collaborated on the rules for a naval warfare game, Don’t Give up the Ship! In 1971 Arneson introduced Gygax to role-playing with his game Blackmoor, set in a dungeon inhabited by monstrous creatures.

It took three more years to complete Dungeons & Dragons, in which players exercise their free will to determine their course through an adventure constrained only by the limits of the dungeon and their imaginations.

The game is played with pencils, paper, multisided dice and a thick rule book, with campaigns that can last for days. It appealed chiefly to geeks; intelligent, socially awkward young men. Initially, it failed to find a publisher, and since neither Gygax nor Arneson, who was working as a security guard, could afford to fund it, a friend came up with the money for the intial print run of 1,000 copies — it sold out within months.

As the game’s popularity grew, Arneson joined Tactical Studies Rules (TSR), the company founded by Gygax and Don Kaye to develop Dungeons & Dragons, as director of research in 1976. But he came to feel that money sucked the fun from game developing and left a year later to work independently.

When TSR published the more complicated Advanced Dungeons & Dragons in 1977 Arneson filed the first of five lawsuits over crediting and royalty rights. A settlement was reached in 1981 awarding Arneson co-authorship.

The legal action affected his friendship with Gygax, but did not destroy it. They were reunited in the mid-1980s when Arneson developed modules for Dungeons & Dragons based on his original Blackmoor version of the game. Arneson and Gygax traded “get well” cards after suffering strokes in 2002 and 2004 respectively.

In 1978 Arneson set up a computer company, 4D Interactive Systems in St Paul, Minnesota, to develop games and educational, industrial and medical software, and later set up his own successful game company, Adventure Games. He continued to develop games including Adventures in Fantasy, with his long-time gaming partner Richard L. Snider, which he envisaged as the game to recapture the original spirit of role-playing fantasy.

For Arneson, fantasy and fun were always at the centre of the gaming experience. So were practical jokes: he once took six friends into the basement to debut a monster called The Blob, he switched off the light and screamed as though he were being killed, then turned it back on to see how each had reacted.

He taught game design at Full Sail University in Florida. While believing that a good game is built on a solid set of rules, he was sceptical about players who were addicted to rulebooks. He said he never used a Dungeons & Dragons rulebook because he always had a newer set of rules in his head.

Arneson continued role-playing well into his final years until falling ill with cancer two years ago. He is survived by his daughter.

Dave Arneson, co-creator of Dungeons & Dragons, was born on October 1, 1947. He died of cancer on April 7, 2009, aged 61