Scientology celebrities are as common these days in Hollywood as, perhaps, vegetarian celebrities or British celebrities. Scientology is a religion that is based upon the teachings of its founder, L. Ron Hubbard, who also developed the concepts of "Dianetics." Some of Scientology's fundamental beliefs are centered around humans being both spiritual and immortal, and humans not being restricted to just one life. Some of the biggest stars on the planet are devout followers of the Scientology religion.

  1. Superstar Tom Cruise is perhaps the most well-known Scientologist of them all. The Syracuse, New York-born actor has been a major presence in cinema since the early 1980's, and was introduced to the religion in the late 1980's by his ex-wife, actress Mimi Rogers. Tom Cruise is best known for movies such as "Top Gun," "Risky Business," "Mission: Impossible" and "Jerry Maguire."

  2. Vocalist, dancer and actor John Travolta as also been an active voice for Scientology since the middle of the 1970's. His wife actress Kelly Preston is also a Scientologist. John Travolta began his relationship with the religion upon reading L. Ron Hubbard's 1950 self-help guide, "Dianetics." Some of the star's most memorable roles include "Pulp Fiction," "Grease," "Look Who's Talking" and "Saturday Night Fever."

  3. Kirstie Alley is a Kansas-bred actress who has been active in television and movies since the early 1980's. The actress, who became a breakout sensation with her role on the 1980's sitcom "Cheers," has been a proponent of Scientology for years, although she grew up as a Methodist. Some of the actress' most noteworthy movies and television programs include "Deconstructing Harry," "Look Who's Talking" and "Veronica's Closet."

  4. Giovanni Ribisi is an Italian-American Los Angeles native that has been a cinematic fixture since the middle of the 1990's, although he got his start in acting as a young child on television shows of the early 1980's. The actor is a devoted Scientologist as is his twin sister Marissa, who is married to another famous Scientologist, the indie rock musician Beck. Some of Giovanni Ribisi's notable films include "Avatar," "Boiler Room," "Gone in Sixty Seconds" and "Saving Private Ryan."

-Isabel Prontes