Thetan
In Scientology, the concept of the thetan () is similar to the concept of self, or the spirit or soul as found in several other belief systems. The term is derived from the Greek letter Θ, theta, which in Scientology beliefs represents "the source of life, or life itself." In Scientology it is believed that it is the thetan, not the central nervous system, which commands the body through communication points.Thetans have been described in the Church of Scientology in a number of ways.

A "thetan is an immortal spiritual being; the human soul."
"The being who is the individual and who handles and lives in the body."
"A thetan is not a thing, a thetan is the creator of things."
A thetan is "the person himself—not his body or his name, the physical universe, his mind, or anything else; that which is aware of being aware; the identity which is the individual. The thetan is most familiar to one and all as you."According to the Church of Scientology, the concept for the thetan was first discovered in the early 1950s by L. Ron Hubbard, drawing on reports by Dianetics practitioners of past-life experiences.