Rettig was an old enemy of Jack Moffitt. Early in World War II, he was a Wehrmacht colonel attached to the Blitzkrieg into France. Following the routing of British forces at Dunkirk, Rettig was given the task of finding and capturing any surviving British troops who hadn't managed to escape across the Channel. Moffitt was one of those soldiers. Wounded, he'd been taken in by a French farmer and his daughter Gabrielle. He fell in love with Gabrielle and the two become lovers during Moffitt's stay at the farm.
Colonel Rettig showed up one day with two men searching for Moffitt. Rettig developed a romantic obsession with Gabrielle, and attempted to first persuade her to help him and his men hunt Moffitt down, and then to agree to a date with him. She refused on both accounts, while her father managed to smuggle Moffitt away from the Nazis in his wagon. Refusing to take no for an answer, Rettig kept hounding Gabrille long after Moffitt was gone, even going so far as sending the Gestapo after her when she tried to escape his clutches. Despite Rettig's repeated interference in her life, Gabrielle managed to join the French Resistance and even marry a French rocket scientist named Pierre.
Rettig's rage broke all bounds at Gabrielle marrying another. To escape him, the couple fled to Africa. For two years they lived in peace until the Germans invaded. Rettig was by this time an officer in the Afrika Korps, having been promoted to the rank of general, allowing him far more power to try and force Gabrielle to have him. When the Germans captured Pierre in an effort to force him to work on the Nazis' rocket program, Rettig saw this as a perfect opportunity to get even with Gabrielle for rejecting him. Despite the fact his superiors needed Pierre, Rettig contacted Gabrielle and offered to free her husband if she would be his.
Gabrielle tentatively agreed. Unaware of this, the Resistance requested the assistance of the Rat Patrol, including her former lover Moffitt, to get Pierre out of the Germans' hands. At the meeting to exchange herself for Pierre, Gabrielle found herself reliving the past as Moffitt showed up in an effort to help her as she'd helped him two years ago. Releasing Pierre, Rettig then attempted to kill Moffitt, even as Gabrielle pleaded for the Englishman's life, as he hadn't been part of their arrangement. As the two argued, Moffitt was able to get the drop on Rettig and attack him.
As the two fought, the other Rats showed up and killed all of General Rettig's men. Rettig knocked Moffitt down and drew his sidearm. However, as he prepared to kill his old rival, a shot rang out. Rettig fell dead, killed by Gabrielle with a gun she had hidden on herself.