Which emperor established the Tetrarchy system with four co-rulers? (r. 284-305 AD)

The story behind the answer

Diocletian (r. 284–305) established the Tetrarchy to stabilize the empire after the Crisis of the Third Century. In 293 he created a system of two senior emperors (Augusti) and two junior emperors (Caesars), splitting administration between East and West to respond faster to invasions and rebellions. This power-sharing aimed to end succession chaos and strengthen frontier defense.

He also reformed taxes, the army, and bureaucracy, and uniquely abdicated in 305. Though the Tetrarchy later unraveled, Constantine emerged from its struggles to reunify the empire. Memory tip: Tetra = four; Diocletian “divides and delegates” to 2 Augusti + 2 Caesars.