Greg Costikyan (born July 22, 1959, in New York City), sometimes known under the pseudonym "Designer X", is an American game designer and science fiction writer. Costikyan's career spans nearly all extant genres of gaming, including: hex-based wargames, role-playing games, boardgames, card games, computer games, online games and mobile games. Several of his games have won Origins Awards. He co-founded Manifesto Games, now out of business, with Johnny Wilson in 2005.
Greg Costikyan is the son of attorney and politician Edward N. and Frances (Holmgren) Costikyan. He married Louise Disbrow (a securities analyst), September 4, 1986. Costikyan lives in New York City near his three children and is a 1982 graduate (B.S.) of Brown University. He is a frequent speaker at game industry events including the Game Developers Conference and E³.