Where is he from?

Teal'c is a member of the alien race known as Jaffa, of the home planet Chulak. Similar to humans in overall appearance, Jaffas have an "X" shaped incision or marsupial pouch in the abdomen. When a Jaffa reaches approximately eight years of age, a Goa'uld larva, the infant form of a parasitic being, is placed in the Jaffa pouch in order to mature.

Differences

There is a strong symbiotic relationship between them as the Jaffa is guaranteed powerful healing abilities and immunity to myriad diseases including all viral or bacterial infections for as long as he carries the symbiote. For this reason, Jaffa live to be very old. Teal'c, although he looks much younger, is actually over 90 years old. After a seven year gestation period, the mature Goa'uld parasite seeks out a new host, (usually human). All Jaffa have a mid-forehead tattoo or symbol indicating that they carry a Goa'uld symbiote.

Friends and Foes!

The Serpent Guards are the elite or royal guard of the Jaffa in service to the Goa'uld Apophis. They wear the heavily armored "serpent head" helmets. Teal'c had served as the First Prime of Apophis, but after aiding the SG-1 team during their first mission to Chulak, he left his family and culture behind and returned to Earth as a voluntary member of the SG-1 team.

His main reason for joining SG-1 was to try to set straight the misdeeds of his past, and to win freedom for his people from the Goa'uld.