Answer
Emperor Xian, the last emperor of the Eastern Han dynasty, was the ruler to whom Lü Bu pledged loyalty. Lü Bu, a prominent warlord during the late Eastern Han period, was known for his exceptional combat skills and political maneuvering. Despite his military prowess and strategic alliances with various factions, Lü Bu's loyalty was often fickle, and he frequently switched allegiances among competing warlords and imperial figures.