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's pack.

This pack consists initially of three wolves, Jacob Black, Seth and Leah Clearwater. In the novel, Embry Call and Quil Ateara V joined after tension between the Cullens and the Uley pack was resolved. At the end of 2006, both packs take in new members due to the increasing number of vampires. While Jacob is the Alpha, Leah and Embry act as his right and left hands, respectively.

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 followed, 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's and Sam's packs resolved their tension when Jacob imprinted on Renesmee Cullen. In Breaking Dawn - Part 1, when a fight ensues between the Cullens and the Uley pack, Leah and Seth run to their Cullens' defense, equaling their strength until Jacob emerges to tell Sam about his imprinting on Renesmee, which stops the battle completely.

Afterwards, Jacob's pack claims the protection of La Push and the Cullens as their jobs, joined by Embry and Quil in the novel. 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 Sam's pack; the plan is cancelled when Jacob imprinted on Renesmee, and he officially embraces his position as Alpha male and the responsibilities that come with it.

When the Cullens are threatened by the Volturi and gather their vampire friends for assistance, Jacob begrudgingly tolerates their allegiance for Renesmee's sake, and has Leah, Quil, Embry and Seth temporarily run with Sam's pack to avoid conflicts. The pack also gains new members due to the increasing number of vampires.

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 also grown in number. 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.

After the Volturi retreated, the pack celebrates their victory with their allies, then retreat to their territory.

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 "Beta". At the end of Breaking Dawn, the pack has gained three unnamed young members. According to The Twilight Saga: The Official Illustrated Guide, Embry is the third-in-command.

In the movie, Quil and Embry seemingly remain in Sam's pack, though Jacob does take in three new members.

Other members
Near the end of Breaking Dawn, the Black pack takes in three new members due to the additional vampires in Forks, which forces some very young tribe members to turn.