In high school civics I was taught that, in America, the president has many roles, often divided in other countries. He's commander in chief, head of state, chief administrator and executive, the head of his party, chief diplomat, legislative leader and, according to some lists, “the guardian of the economy.”
I think we need to add another job description: He's the talent.
In Hollywood — and increasingly journalism, business and government — “the talent” is the person who must be catered to above all others. With few notable exceptions, you can get another executive producer or director, but you can't get another Barbra Streisand or Arnold Schwarzenegger.