The reborn gatekeepers of Vishnu, Jaya and Vijaya.
Dantavakra is Vijaya, Shishupala is Jaya.
Shishupala was the son of the royal couple of Chedi, Damaghosha and Shrutshrava. He was born with three eyes and four arms. His parents wanted to abandon him, but a heavenly voice prophesied that a man would come to take him on his lap and that he would lose the unnecessary parts. Later this man will kill him. The man was Krishna. The mother asked Krishna not to kill her son. Krishna gave Shishupala 100 insults, at the 101st he would kill him. This happened at the consecration of Yudhishthira, where Krishna was invited as a guest of honor and Shishupala defamed him as a cowherd. The hatred arose mainly because Krishna once married his bride, Rukmini.
Dantavakra was the son of Vridhasaman and Prithudevi, Karusha kingdom. He was born with protruding, crooked teeth.
Read about Shishupala and Dantavakra here