The Army of God (AOG) is a name that has been and is used by multiple groups. Ignoring possible uses for historical military crusades, the term was first coined when Don Benny Anderson kidnapped an abortion doctor and his wife, promising to release them if abortion would be outlawed in the United States.
AOG does not claim to be an actual organization, but rather, a like-minded group of Christian militants who have committed violent acts against abortion doctors and abortion clinics. It is guessed to be a nebulous Christian terrorist group that is far right-wing and advocates violence. They have been known to attack the abortion providers and abortion clinic staff, as well as praising the beheadings of homosexuals in Saudi Arabia.
Salon - The Quiet Fall of an American Terrorist - Summary of the activities of an anti-abortion fanatic Clayton Waagner, who used packets of bogus anthrax to shut down scores of clinics nationwide, plus a remarkable lack of news coverage upon his conviction.
Text of Letter from `Army of God' - The text of a letter by a group claiming responsibility for a bombing at an Alabama women's clinic.