Answer
Manuel I Komnenos, the Byzantine emperor, earned the epithet "ho Megas" from the Greeks during his successful reign from 1143 to 1180. Known for his military prowess, Manuel expanded the Byzantine Empire's territories, skillfully defended against various adversaries, and strengthened the empire's economy and cultural standing. His accomplishments and leadership qualities left a lasting impression, leading to the Greeks honoring him with the title "the Great."