Monte Cook (also known as Monte Cock, Monte Kook and Monte Cuck) is one of the big daddies of modern tabletop RPG game design, alongside such figures as Robin D. Laws and Keith Baker, because having a name like an action movie actor/character is apparently a prerequisite of the "Game Designer" class. He is one of the founding creators of Dungeons & Dragons 3rd Edition, which helped convince the community that the IP was in working hands after the demise of TSR, and has done lots of work writing his own games and version of other games, including a personal take on the World of Darkness (that everyone hated) and Numenera, a game set on Earth a billion years into the future, that served as the prototype for his Cypher system. (Basically FATE d20 edition.)
As a game designer, Monte Cook is known for four major things: being a genuinely brilliant and insightful setting designer who crafts fun and imaginative systems and games, having a profusion of "cool" ideas that need the assistance of partners to help filter out the good one from the bad, regularly quitting and re-joining the industry every few years over disputes with the management, and for having an insane, out of control spellcaster fetish beyond all expectation or reason. In fact, he once infamously said that the biggest tweak 3rd Ed. needed was a hard nerf to all martial classes, particularly the fighter, and an across the board buff to all spellcasters. Yes, we are talking about the same 3rd Edition in which half the classes in the game were better fighters than the fighter, and spellcasters could pull shit like this. (While theoretically he has a point, since at level 1 the spellcaster classes are a bit suck, most would argue that a stabler power curve where magicals start higher and martials suck less later would be the ideal solution, rather than ensuring the wizard dominates at all levels of play.)
One thing people like to hold his feet to the fire over is the "Ivory Tower" school of game design: since he was working for a company that literally made its name with card games, why not put in systems to mimic card games? The "Ivory Tower," or "system mastery" for those that don't hate it, involves deliberately sowing weak "newb traps" into your game as character advancement options (explicitly compared to "Timmy cards"), to punish new players for the crime of inexperience and offer veterans an inflated sense of self-worth that comes from attaining a wholly artificial sense of "mastery." To his credit, he has since apologized for the whole thing and admitted it was a terrible idea from start to finish, but here we are, still scrubbing through the aftermath years after the fact.
Still, it could be worse. At least the personality that seeps into his work is warm and fun rather than smug and unpleasant.