The thief in the title of Thief of Time, a Discworld novel. He becomes the apprentice of Lu-Tze, and the first to figure out all of his five suprises. With the help of Susan (Death's granddaughter) and Lady Myria Lejean, Lobsang and Lu-Tze save the world from the auditors.
Named Nougat Ludd at finding, he was one of Ludd's Lads and Lasses, a Monk of History, and a member of the Brotherhood of the Basket. A foundling left on the steps of the Thieves Guild, he grew up to have a very successful career as a thief, found religion, and then took over his mother's job.
The son of Time, he is also the brother of Jeremy Clockson. This is, in fact, a lie. It is a lie that makes the truth easier to understand. To describe the two of them as twins is conceptually a lot easier than the reality, which is that they are the same person in two different bodies. Nanny Ogg, the best midwife of all time (though it took three tries to find her at the right time), describes their situation to Susan like this: "twins is two souls born at once, not one soul born twice."
When you consider that human wasn't a shape that came naturally to their mother (not being natural), their curious circumstances of birth begin to make more sense.
Thief of Time