In this American site,which is the source I have chosen to introduce the caste system, you will find a very good overview of world religions. If you look at Hinduism, you will understand the origin of the caste system.
This diagram shows the classes of the Hindu caste system in India with Brahmins being at the top.
The Caste System is a rigid class structure based on Hinduism which is found in India. It is believed that if one leads a good life, following good karma and dharma, then they will be rewarded by being reincarnated as a person belonging to the next highest level in the Caste System. However, if one is wicked during their life, they will be demoted, and possibly even removed from the Caste System altogether. Outcasts, or Untouchables, are members of Hindu society thought to have been removed from the Caste System, with no hope of returning to it, due to their misdeeds in previous lives. Work that is deemed unclean for all other Hindus is reserved for these Outcasts. After winning its independence from Great Britain in 1947, India adopted a national constitution which stated that “Untouchability is abolished and its practice in any form is forbidden.” Since that time many Caste reforms have been enacted to diminish discriminatory practices in India. Today, the Caste System still exists in practice, despite the many laws designed to legally abolish it.
Watch these videos and identify the different castes