Zaxweqrahh Ainahilla was a renegade time lord from the planet Gallifrey. He was the son of the Doctor but he had an evil nature. He is the father of Susan who was the Doctor's granddaughter. Zaxweqrahh's father may have been a good man but he was nothing like his father because of his evil personality. During the time war Zaxweqrahh betrayed Gallifrey becoming a servant of the daleks and later he even became a dalek believing that he would live forever that way having a thirst for immortality.
Zaxweqrahh was the son of The Doctor and Valkyrie a time lady. Not much is known about his early life except that he attended the time lord academy and was a troubled child. Zaxweqrahh became evil and betrayed the time lords and he believed that not even time lords could live forever and he longed for immortality so he betrayed the time lords as a servant to the daleks in the time war and even was enhanced having a dalek form. When the dalek fleet ship exploded, Zaxweqrahh ended up on Earth in 19th century London and was repaired and enhanced by an Italian inventor resembling a steam punk style dalek. Zaxweqrahh became a weapon for the British army during that era but later run away refusing to be a servant for humans. Zaxweqrahh later met the Doctor in his eleventh incarnation and The Doctor told him "I can't believe you." He was ashamed of his son's betrayal to Gallifrey and tried to change his evil ways but Zaxweqrahh then exterminated The Doctor causing him to regenerate into his Twelfth Incarnation. The Twelfth Doctor foiled Zaxweqrahh's evil plan to enslave humanity and bring back the dalek race but he did it with sadness having no choice but to destroy Zaxweqrahh. Zaxweqrahh later survived and possessed Nolan Green a troubled teenage book nerd who believed in time lords living in present day London. In Nolan's body he was then again confronted by The Twelfth Doctor. The Doctor was unable how to exorcise Nolan freeing him from Zaxweqrahh's control. Eventually with the help of an eccentric librarian who also thought time lords were real he was able to separate Zaxweqrahh from the body of Nolan reducing him to a normal kid once again and Zaxweqrahh with no physical form. Zaxweqrahh later possessed the Harold Saxon master and yet again attempted to enslave the UK but was foiled by the Doctor.