Not wanting to get too off topic, and Ingo might know more than I do, but IIRC, Sagat was the champion of the street fighter tournament (SF1) he lost to Ryu, who gave him the scar. Sagat then became obsessed with beating Ryu, so he joined up with Bison and his group to get another chance to fight Ryu and beat him. So they are pretty bitter enemies, or at least from Sagat's point of view they are.
Not wanting to get too off topic, and Ingo might know more than I do, but IIRC, Sagat was the champion of the street fighter tournament (SF1) he lost to Ryu, who gave him the scar. Sagat then became obsessed with beating Ryu, so he joined up with Bison and his group to get another chance to fight Ryu and beat him. So they are pretty bitter enemies, or at least from Sagat's point of view they are.