United States Senate Majority Leader
Unlike the Speaker of the House, the Senate Majority Leader is not a position established anywhere in the Constitution — so take that, bitch! Instead, the position arises from the tradition of the Senate. Also in accordance with tradition, the Senate Majority Leader must occasionally stand on a roof of the Senate and play the fiddle — this is especially true if Rome happens to be burning.
The official presiding officer of the Senate is the Vice President, but since no one can remember who he is — not even the Vice President — that duty falls on the President Pro Tempore of the Senate, the Senator who has worn adult diapers for the longest period of time. By tradition, however, he will defer to the Majority Leader for fear that the Majority Leader will use the Majority Whip on him.
The Majority and Minority Leaders of the Senate are elected within their individual partisan assemblies in an ancient, arcane and disgusting fashion that cannot be discussed here. The victor of this death match becomes... er... did I say death match? That's not what I meant. You didn't hear it from me.
The victor of the secret selection process in each party becomes that party's Floor Leader. The party that can beat the other in a game of round-robin ping-pong then becomes the Majority Party and its Floor Leader becomes the Majority Leader.
The Majority Leader runs the business of the Senate, deciding who can speak, what bills can be voted on, and assigning random depantsings to the Junior Senators. In recognition of this fact, the Majority leader gets a seat at the front of the Senate and gets to sit in the front of the bus during field trips.