He and his
 co-emperors Maximian, Galerius, and Constantius each ruled one quarter of the empire in a system called
 the Tetrarchy.
To become emperor, he won the Battle of Margus after his predecessor, Carus, was struck by lightning.
 In one story, this emperor was asked to return to the throne but decided he was happier living as a cabbage
 farmer at his palace in Split. Rapid inflation prompted him to introduce a coin called the argenteus and
 establish price controls with his Edict on Maximum Prices. He is remembered for allegedly martyring
 20,000 people at Nicomedia, an action later outlawed by Constantine's Edict of Milan. He and his
 co-emperors Maximian, Galerius, and Constantius each ruled one quarter of the empire in a system called
 the Tetrarchy. For 10 points, name this Roman emperor noted for persecuting Christians.
To become emperor, he won the Battle of Margus after his predecessor, Carus, was struck by lightning.
 
Diocletian