Agha was a general of Kamsa, uncle of Lord Krishna, and he was deputed to kill Child Krishna at Vrindavan. Aghasura also had a personal score to settle with Krishna as he was the brother of Putana. She was killed by Krishna when she attempted to give poisoned breastmilk. To fulfill his mission, Agha took the form of a huge snake and arrived at Gokul.
After scanning the activities of Krishna and friends, the demon opened his mouth and stood still. Now the demon looked like a cave. Lord Krishna’s friends ventured into the demons mouth to play, thinking it was a new cave that they had not discovered.
But little Krishna sensed the hidden danger and he was able to rescue his friends before the demon could close his mouth. Then a battle ensued between demon Agha and Krishna . Little Krishna easily overpowered the demon and killed it.