Triumvirate

Definition: a ruling body of three parts

This refers to any authority structure that consists of three people. Apparently this has been so common throughout history that it has its own word.

It’s Latin for “three men.”

Why I Looked It Up

From Stalin's Library: A Dictator and His Books:

…Trotsky organized a campaign within the party that accused the Polituro majority, headed by a triumvirate of Stalin, Zinoviev, and Kamenev, of constituting a “factional dictatorship.”