Caleb was born in Nebraska, USA. His entire family were military related and he had 2 older brothers.
During the battle of patience creek, Caleb used his Duplication Legacy to create a twin brother for himself, calling the duplicate "Christian." When the Piken Mog attempts to kill Caleb, John, Sam, Walker and Lawson, Caleb sends "Christian" to attack, and after Christian is revealed to be a duplicate of Caleb, Lawson encourages Caleb to create two more duplicates to attack the Piken-Mog. After they escape the facility with Number Five, Daniela, and others, John and Six order Caleb, Nigel, and Ran to lead the Human-Garde as the leaders of tomorrow. John also gives Caleb the Chimæra Regal, who lands on his shoulder in hawk form.
During his time at the academy, Caleb struggles with control of his duplicates. It is suggested he previously had multiple personality disorder, which manifested in his duplicates. When Nigel asks him if the voices ever stop, Caleb replies "Never", suggesting that the duplicates are always arguing in his head.
At the end of Generation One, Caleb starts a band with Nigel and clones, in an attempt to help control the duplicates a little better.
His other Legacy is Duplication. It allows him to make a clone of himself that he can control. However due his multiple personality disorder, his clones can have a mind of their own and sometimes even pop out of Caleb without him using his Legacy. This happened in Patience Creek whereas everyone thought he had a twin brother named "Christian" that was always so silent without knowing that his supposed twin is just a clone. Each clone tends to have its own personality, Caleb referring to them as 'Reasonable-Caleb' 'Mean-Caleb' and so on. To date, Caleb is able to manifest a dozen clones at once, but it takes its toll and he is not able to keep it up for too long. He can control the clones as a group, but each one will act in its own personality unless Caleb steps in to control it specifically.