Many happy returns on the 7th of November to the following three actors who between them have been on all three live action series.
John Aylward who played President Nadal in the Stargate SG1 season 9 episode Ethon. He has also been in Fringe and ER. IMDB
Josh Blacker played the troubled Sgt Spencer in Stargate Universe also a guest spot in the Atlantis episode Vengeance. IMDB
In the real world aside from acting he is a Paralegal
Dakin Matthews played was Maz’rai in Stargate SG1 Stronghold also roles on True Blood and General Hospital. IMDB