Black pack

The Black pack, also known as Jacob Black's pack, is formed when Sam Uley and his pack planned to kill Bella and Renesmee in Breaking Dawn, and prompted Jacob to embrace his rightful position as Alpha and break away from Sam. This pack consists initially of three wolves, Jacob Black, Seth and Leah Clearwater, but later Embry Call and Quil Ateara V joined to be with their friends. While Jacob is the Alpha, Leah and Embry act as his left and right hands.

Breaking Dawn
In Breaking Dawn Jacob was ready to kill Renesmee, but could not do so with Bella for he still had feelings for her. Sam planned to kill Bella to prevent whatever offspring she carried from being born, for the protection of humanity, and forced Jacob to obey when he refused. By accepting his rightful place as Alpha and refusing to take Sam's place in the pack, he decides to go rogue, but Seth Clearwater soon joined, not thinking it was right to attack their allies with no warning nor provocation. His sister Leah joined soon afterwards to get away from Sam Uley and the memories of their failed relationship, and wound up becoming the pack's Beta. They were instrumental in helping the Olympic Coven hunt in case Sam's pack was out looking for the Cullens and also to protect Bella during her pregnancy. Jacob and Sam's packs resolved their tension when Jacob imprinted on Renesmee.

Afterwards, Jacob's pack claims the protection of Forks and the Cullens as their jobs, with Embry and Quil on their side. While Jacob originally wanted to live as a wolf for a while and Leah decided to stay in his pack, the rest of the pack was bound to return to La Push; the plan is cancelled when Jacob imprinted on Renesmee.

This pack stands beside the Cullens and their allies during the confrontation with the Volturi. They were also joined by Sam's pack which had grown in number since Jacob left. On this occasion, it is revealed that the pack is actually composed by shapeshifters who could change into wolves, and not actual werewolves. Unbeknownst to them, they are all under protection when Bella uses her shield to ward off the Volturi's powers.

Members
In addition to Jacob, Seth and Leah, the pack comprises Embry Call and Quil Ateara V. Leah eventually became the second-in-command of the pack, which Bella Swan called the "Beta". According to The Twilight Saga: The Official Illustrated Guide, Embry is the third-in-command.