Shaun Allen is a 13-year-old CHERUB. He is commonly known as a nerd and a loner.

Born Thomas James Gibb in 1999, Shaun was born and raised in South Manchester. His mother walked out on the family due to his father (Alan Gibb)'s cocaine addiction when Shaun was only one year old, and he grew up on a council estate with his father and two older brothers, Chris (then eleven) and Will (then sixteen).

As a drunk and a drug addict, Shaun's father never had a good relationship with his sons. As the youngest and therefore the weakest, Shaun took more bullying than his brothers. He was often beaten up by his dad. The three brothers formed a close bond, and when Will was eighteen and about to move out, he tried to take his brothers with him. However, Alan found out and attacked Will. Will was killed in this attack. Too scared to tell anyone, all Shaun and Chris could do was keep the attack secret and live in fear of the same happening to them.

When Shaun was four, he discovered computers. He visited the local library and spent until closing time on the computer. The next day, he came back and waited two hours in the freezing cold for the library to be open; he was desperate to get back on the computer. He spent the whole day on the computer.

After this, he became obsessed. When one of Chris' friends offered Shaun an old computer that he no longer needed, he jumped at the chance. By the age of five, he could install programmes with ease. At seven, he had developed basic hacking skills.

It was when Shaun was seven that his father died. He was stabbed in a drunken brawl. Shaun and Chris - who was seventeen by now - moved into a children's home. However, Shaun was often picked on - both at the home and at school - because he was thought of as a nerd. Chris tried to protect Shaun, and constantly got into fights bcause of this. It was in one of these that he was killed - stabbed, just like his father had been. Shaun now had no living relatives - his mother's side of the family were completely unknown, his brothers, father and grandparents were dead, and his father had been an only child. He became depressed and started to see a counsellor. The counsellor worked for CHERUB...

On his third counselling session, he was drugged and awoke at CHERUB. He passed the tests fairly easily, with the exception of almost failing at the obstacle course due to extreme nerves. At CHERUB, he changed his name from Tom Gibb to Shaun Allen, keeping his middle name of James. He earned his navy T-shirt in a mission that foiled an assassination attempt on Barack Obama; a mission in which his hacking skills were vital.

However, since returning from the mission Shaun hasn't been involved in any more.

His leg was badly burnt in an attack from Kenny Angel. After he impulsively kissed Michi Vulcan, Michi stormed off to Selene's room to find Kenny. After going there to say sorry to Michi, Selene got angry at him and so he floored her. Kenny then threw a lighter at him in retaliation.

This incident mentally scarred Shaun. He now suffers from depression. He has cut himself and is contemplating taking drugs, but as of yet has not taken any.