Who was the Eastern ruler from whom Constantine fled?

The Eastern ruler from whom Constantine fled was Galerius. Galerius was a prominent figure during the Tetrarchy, the system of governance established by Diocletian, which divided the Roman Empire into multiple regions ruled by different emperors. His tenure was marked by significant persecution of Christians, and his relationship with Constantine was strained due to political and personal rivalry.

Constantine initially faced challenges in his rise to power, including conflicts with Galerius, who was an established emperor in the East. After Galerius's death, the political landscape shifted, allowing Constantine to consolidate his power, ultimately leading to the end of the Tetrarchy and his ascent as the sole ruler of the Roman Empire. This context reinforces why Galerius is the correct answer as the ruler from whom Constantine fled, rather than other figures like Diocletian, Maxentius, or Licinius, each of whom held different roles and contexts in the history of that era.