For the uninitiated, Abhimanyu was the youngest son of Arjuna and Subhadra, the characters of Mahabharata. He was the nephew of Lord Krishna and was married to Uttara, the princess of Matsya Kingdom.
Abhimanyu was the reincarnation of son of moon-god(Chandra). When the moon-god was asked to let his son incarnate himself on earth, he made a pact that his son will only remain on earth for 16 years as he could not bear to be separated from him. Abhimanyu was most loved of all sons of Pandavas. Draupadi used to love him more than her own sons. Draupadi once said that if Pandavas are not willing to wage war, then her sons lead by Abhimanyu will attack and get justice for her.
He was the one who entered the powerful Chakravyuha battle formation of the Kaurava army.
Source of Information : Wikipedia