Kerrigor Timeline and Summary

Kerrigor was born Prince Rogir, maternal half-brother of Touchstone. He travels the kingdom studying Free Magic, eventually becoming one of the Greater Dead. He hides his body in Ancelstierre and used Free Magic to assume human form.
He sacrifices his mother and sister on the Charter Stones in the capital city in order to break the stones, effectively ending the royal line, apart from Touchstone. When he does this, the then-Abhorsen banishes him into Death.
Refusing to stay dead, Kerrigor returns to capture newborn Sabriel and bring her into Death, but her father rescues her, sending Kerrigor once again into Death.
Kerrigor vows to return, and he does—he reappears at the site of the broken Charter Stones in the Capital City, trapping Sabriel's father in Death.
Sensing Sabriel is on her way, Kerrigor sends one of the Greater Dead, a Mordicant, to kill her on her journey; when this doesn't work, he appears at the underground reservoir once more. Sabriel's father banishes him into Death again with Astarael, dying in the process.
Kerrigor reappears at Wyverley College with a supporting crew of zombies, determined to stop Sabriel performing Final Rites on his body. He manages to kill her, but not before she destroys his body and traps him in the form of a cat. Cat Kerrigor probably isn't going to be a very pleasant pet.