I've recently finished reading Gaius Marius: The Rise and Fall of Rome's Saviour.

Marius rose from humble beginnings to be elected consul and to become the most powerful man in Rome. It's an excellent biography of a man who was a brilliant general, but a ruthless politician, as was his rival and worst enemy Sulla. Marius was Julius Caesar's uncle by marriage, and his friend Cinna was the father of Caesar's first wife.