Who was monks? How was he related to Oliver and why did he want Oliver to become a thief?

Monks is a a minor character and villian in the story. He is actually the half-brother of Oliver Twist, but he hides his identity. The father's will favours Oliver, and not Monks. There is a catch though: if Oliver should ever commit a crime, he will be automatically disinherited, and everything in the will goes to Monks.