Like Han Solo, Crix Madine was a Corellian. Instead of a life of smuggling and . . . casual living, however, Madine was always destined for a military life.
His career began at Raithal Academy, after which he graduated into the officer corps of the Imperial Army. There, he pioneered the use of a surgical strike team, known as the Storm Commandos, to counter Alliance guerilla fighters. The unit drew the attention of the higher echelons of Imperial command, and soon the unit was being asked to perform more and more tasks.
Unfortunately, Madine found the morality of these new assignments questionable. He defected to the Alliance just prior to the Battle of Yavin, where his intimate knowledge of Imperial practices served him well.
Despite his eagerness to prove himself a valuable part of the Rebel Alliance, there were always those Rebels who didn't quite believe that such an influential member of the Imperial command has actually defected. Most of these doubts were quashed once the support of General Carlist Riekan propelled him into the Alliance High Command.
There, he became the resident expert on the use of special forces. Indeed, his manual, Madine's Rules of War, became the standard reference work given to new Special Forces recruits.
He, and Special Forces under his direct command, were responsible for the capture of the Imperial shuttle, Tyderium. This craft was used by Han Solo and Princess Leia to evade Imperial reprisal and land on Endor. Once landed, the plan Solo used to take down the shield around the Second Death Star was, with a few of his team's own improvisations, one authored by General Madine.
After the Battle of Endor, Madine rose to the post of Supreme Alliance Commander for Intelligence. Despite this high office, he continued to actively lead troops on the ground. In one such mission, about 7 years after the Battle of Endor, he was killed by Durga the Hutt while gathering intelligence on the Darksaber project.