Donald R. Kaye (June 27, 1938 – January 31, 1975) was the co-founder of Tactical Studies Rules (TSR), the game publishing company most famous for their Dungeons & Dragons (D&D) role-playing game. He and TSR co-founder Gary Gygax had been friends since childhood, sharing an interest in miniature war games. In 1972, Kaye created Murlynd, one of the first D&D characters, and play-tested him in Gygax's Castle Greyhawk campaign. Kaye and Gygax were convinced that D&D and similar games were an excellent business opportunity, and together they founded Tactical Studies Rules in 1973. However, only two years later, just as sales of D&D started to rise, Kaye unexpectedly died of a heart attack at age 36.