JPMorgan Chase shows that two CEOs can be better than one.

These two told their boss Jamie Dimon to fire both of them if either tried to stab the other in the back. The threat of mutually assured destruction has worked so far. Black oversees most of the firm's investment banking efforts, while Winters has responsibility for credit and trading activities.

WINNER: Both. These two are the kingpins of Wall Street right now. 

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PARTNERS: John Mack and Phil Purcell, Morgan Stanley Dean Witter, 1997-2001

After the merger of their respective firms, Purcell surprised many by outmaneuvering wily Mack, who left the company in 2001. Four years later, however, a management revolt resulted in Purcell being shown the door and Mack returning in triumph.

WINNER: Purcell, at first, but Mack prevailed in the end. He is still running Morgan Stanley (MS) today.