This series takes the Stargate movie theme a lot further, introducing us to the parasitic and symbiotic species (called the Goa'uld) of whom the entity known as Ra, the Sun God was but one member.
After the events depicted in Stargate, several teams were set up to explore other worlds via the Stargate: these teams are called SG-1, SG-2 etc. We re-meet Colonel Jack O'Neil—played far more sympathetically (and with a dry sense of humour) than in the original movie by Richard "MacGyver" Dean Anderson—and Doctor Daniel Jackson, played by Michael Shanks who does an excellent job of re-creating James Spader's rôle. They are joined by Major Carter, played by Amanda Tapping.
Very soon they add one of the apparent enemy to the SG-1 team: Teal'C, a Jaffa, who was one of the parasitic aliens' servants and guards, but who has for personal reasons turned against them. He is played superbly by Christopher Judge. Thus we end up with the classic four-person group placed into uncharted territory scenario.
Some of the SG teams are designated for specific functions:
The series has certainly been a success, with its original style of alien technology, the writing and acting, and the fact that it doesn't take itself too seriously; and is now in its fourth season. There is a website for the series here.