MacDonald's history is exactly the same as that of Earth-616's Scorpion up until the Marvel NEW! relaunch.
After finding out about Otto's dying wish, he decided he didn't want to live the life of a villain and joined the army to set his life straight. He heard about the agent venom program and was intrigued and asked Colonel Ross if he would recommend him for the new and improved agent anti-venom program which is designed specifically for rehabilitating bad guys. He showed exceptional progress as the world's Agent Anti-Venom and even earned a place on the Avengers by Captain America himself.