Caleb's History
Calling
Prior to becoming the right-hand man of the First Evil, Caleb was responsible for the deaths of at least two girls, whom he lured with his stirring sermons and masculine charm. One of these was Betty; the second girl was apparently a choir girl in Knoxville, Tennessee. However, the First referred as well to "all these girls" who followed him, implying many more were killed.
In 2002, Caleb was responsible for organizing the Bringers' systematic attacks on the Potential Slayers as well as their respective Watchers. He orchestrated the bombing of the Watchers Council headquarters in England, causing the deaths of its director Quentin Travers and many other members of the Watchers Council, such as Phillip, Lydia, and Nigel.
After the destruction of the Council, Caleb traveled to the United States. He presented himself at a Catholic mission in the town of Gilroy, where he was welcomed and given food, though he disturbed the mission's members because of his rantings about destiny. There, he uncovered a secret room, which bore an inscription that translated to "It is not for thee. It is for her alone to wield". Caleb then turned on his benefactors, burning his mark into one of them and killing the rest.
Caleb seemingly orchestrated as well an attack to the women's prison in Stockton, where he tried to have Faith Lehane eliminated by her fellow inmate Debbie, though the would-be-assassin failed in her task.
Sunnydale
Caleb eventually made his way to Sunnydale, running into a Potential Slayer named Shannon on a highway. The girl had been on the way to the town as well, but was targeted by a group of Bringers who drove her right to Caleb's truck. Believing herself to be safe, Shannon told Caleb she was on her way to Revello Drive. After a sermon, Caleb quickly turned on Shannon, burning his mark on the side of her neck, stabbing her in the stomach, and throwing her to the highway. She was then found by Willow Rosenberg and Faith, who were travelling from Los Angeles in the same road. Before injuring her, Caleb gave Shannon a message for Buffy Summers: "I have something of yours."
Caleb set up camp at the Shadow Valley Vineyards, where the Bringers began to dig in order to find the artifact Caleb had been seeking in the Gilroy mission: the Slayer weapon Mʔ. Due to Caleb's challenge, the Scooby Gang attacked the Vineyard. In the ensuing fight, Caleb murdered two potential Slayers and defeated Buffy, Faith, and Spike. Buffy was able to knock him down temporarily to allow the group to escape; however, before the group retreated, Caleb also managed to gouge out Alexander Harris's left eye with his bare hands. Spike knocked him down to rescue Xander and the group was allowed to escape.
Death
Empowered by a new transfusion of power from the First, Caleb had a final duel against Buffy in the Guardian's crypt, killing the Last Guardian just as she talked with Buffy. The Slayer was armed with the recently retrieved Mʔ, but still had difficulty fighting him enough for him to use the weapon against her. As Caleb prepared to kill Buffy with the scythe, Angel suddenly arrived and knocked Caleb out for a moment, allowing Buffy to recover. She refused further help from Angel, wanting to finish the job herself, and the two resumed the fight. This time, Buffy managed to slice Caleb across the stomach with the Mʔ, apparently killing him.
However, Caleb's recent transfusion of power apparently granted him great endurance, so he rose again and knocked Angel out for a final confrontation with Buffy. While still incredibly powerful, this time Buffy was able to fight more evenly with Caleb. She killed Caleb by using the scythe to cut him vertically from the groin up. As Angel regained conscious, aware Buffy had killed Caleb and ready for another round, Buffy jokingly confirmed that Caleb "split". The First confirmed that Buffy did in fact kill him that time, then being able to assume his form.
Legacy
Some time later, the First Evil appeared to Buffy, manifesting under the guise of the slain Caleb. The night before she went on direct battle against his army of Turok-Hans, the First lectured Buffy on the futility of her campaign against it. Although, this meeting that encouraged Buffy to come up with her plan to activate multiple Potentials worldwide to full Slayer using the essence of the Scythe.
While at the Slayer Organization, Buffy had a recurring nightmare in which Caleb was again alive, in the home of the Seed of Wonder, with her claiming: "I left you in a smoking crater." In the dream, he lectured Buffy while she was devastated by her two vampire lovers, Angel and Spike, kissing each other. The dream changed to Caleb heading the wedding ceremony of Buffy and a skinless Warren Mears.
At the time, Caleb was also one of the red herrings thought to be behind the mask of Twilight. When Buffy attempted to cut Twilight in half by the crotch, he retorted: "I know that move, Slayer." Twilight was eventually revealed to be Angel, who was present when Buffy defeated Caleb with this same move.
