A triumvirate is a group of three people who share power. In America's early days, George Washington, Thomas Jefferson, and James Madison were a triumvirate — three men whose leadership helped shape America.
The prefix tri means "three," so it makes sense that triumvirate refers to a group of three. In this case, the three in question are powerful men who share authority. The word comes to us from ancient Rome, where two groups of three important men shared power over the Roman Republic. The First Triumvirate was made up of Julius Caesar, Pompey the Great, and Marcus Licinius Crassus, and the Second Triumvirate consisted of Marc Antony, Lepidus, and Octavian.