Answer
Galerius, a Roman emperor from 293 to 311, was aided by Diocletian, his co-emperor and mentor. Diocletian, who ruled from 284 to 305, implemented the Tetrarchy, a system of four co-emperors, to maintain stability and control of the vast Roman Empire. Galerius played a vital role in this system, as one of the two junior emperors (Caesars) under Diocletian's rule.