The name Keshi means "long hair" or "horse-man" and the demon was known for his horse-like appearance and strength.
Keshi was sent by the demon king Kamsa to kill Lord Krishna.
However, Lord Krishna killed Keshi by grabbing him by the horns and hurling him to the ground, thereby protecting the people of Vrindavan. As a result, Lord Vishnu came to be known as Keshava, the slayer of Keshi.