Cook is one of the three authors of the third edition of Dungeons & Dragons, along with Skip Williams and Johnathan Tweet. According to the bio on his website, Monte has been a professional game designer since 1988.
Some time after co-authoring the third edition of Dungeons & Dragons, Cook left Wizards of the Coast to write material for the d20 System independently. His most notable recent work is probably Arcana Unearthed, a product he describes as a 'variant player's handbook', alluding to the Player's Handbook of Dungeons & Dragons. Arcana Unearthed enjoyed surprising popularity (or at least high sales) shortly after publication.