Setting: The remnants of Earth (they called it something that started with a "U")
Opening: I recall the book opening with someone with a long name who preferred to only keep the middle part of his name: "Sam."
Important Plot Points: There is a spaceship which includes the word "India" (I can't remember the name). The crew of this spaceship manages to transfer souls into automatons, Percy Jackson-Daedalus style. Doing this creates an immortal race which recreates the caste system and puts them at the very top. I also remember that there are instances of Hindu gods and goddesses present in this book (I think people that sacrilegiously take their names).
Potential Authors: I don't think it's by one of the giants (Bradbury, Asimov, Orwell), but it's by someone less well-known. I feel like I would have remembered the author had it been one of those three.
Approx. Publication Date: Probably early 1970s.
His followers called him Mahasamatman and said he was a god. He preferred to drop the Maha- and the -atman, however, and called himself Sam. He never claimed to be a god, but then he never claimed not to be a god.
This is Lord of Light by Roger Zelazny.
Lord of Light is the story of Sam, an original colonist ("First") of an initially hostile world and his war against the gods.
Long before the story begins, the Firsts arrived from Earth ("vanished Urath") on the ship "Star of India." They fought the native inhabitants of the world to carve out a place for the colonists to live, since they couldn't return. The war took hundreds, possibly thousands, of years with the Firsts living serially in replacement bodies by a process of mind transfer. They developed psychic powers, and refined them to Aspects, which gave them god-like powers. Ultimately they took on god-like personages modeled after the gods of Hindu mythology and created a Celestial City to dwell in.
The book begins with Sam ("Great-Souled Sam") being recalled from the ion clouds surrounding the planet, where his animus was sent by the gods when it was discovered they couldn't kill him by normal means. The god Yama brings him back in order to renew his attack on the gods and overthrow their order.
The story then flashes back hundreds of years to when an aging Sam, in the role of a prince called Siddhartha, rides into a town to get a younger body. He discovers that the gods have been increasingly enforcing a heavy-handed theocracy, stamping out technological advancements and recently requiring tests for disloyalty before allowing transfer to a new body. This is too much for Sam, who walked away from his god-hood, and he decides the time has come to overthrow the old order. (The gods had recently destroyed an entire city for the sin of developing a printing press.)
The first prong of his attack is to draw on his knowledge of Earth, and to establish Buddhism as a response to the Hindu-derived order. He takes on the role of Buddha and begins to preach a philosophy of seeking enlightenment and the path to Nirvana. Certain of the gods see the danger in this and attack him; he is forced into hiding for a while, but his teachings take root.
He makes a pact with some of the remaining native inhabitants, freeing them from their imprisonment in exchange for aid in battle. The gods win the battle, although at some cost; their ranks are depleted. Sam is killed, but thanks to a gift from Taraka, the head "demon," his animus is able to live on and displace another god's animus and steal his body. Sam manages to kill several more gods before he is caught again, and his animus projected into the ion cloud.
The final part of the book rejoins the current time. A re-born Sam, with Yama and a few other rebellious gods and the remaining demons, form an alliance (1) in a 3-sided battle with the main gods (2) and Nirriti the Black (the ex-chaplain of the ship) with his zombie hordes (3). Nirriti is defeated, and the gods are weakened enough that the theocratic order will decay.