A Fixer??

JK: I'm not the guy you kill. I'm not the guy you strongarm, blackball, or fight. I'm the guy you buy! Are you so fucking blind that you don't even see what I am? I sold control of delicate info the club wanted out of circulation for 105 grand. I'm your easiest problem and you're gonna kill me or get your nose bloodied taking me on?

Michael Clayton is what's described as "a fixer". This means that he fixes problems for the firms clients. While, in a sense, all of the firms attorney's fix problems, Clayton specializes in more sensitive issues, ones that sometimes skirt the boundaries of legality or morality. As he explains towards the end he does things like suppress embarrassing photos, convinces the police not to press charges, cleans up drunk or high clients etc etc. He knows all the firms dirty laundry but he isn't a partner (as Karen Crowder notes) and does not practice law in any traditional sense.