A former soldier for the Empire, Crix Madine defected to the Alliance, bringing his Academy training and Imperial insights into the Rebel fold. It was Madine who masterminded a number of crucial Alliance operations that paved the way for victory at the Battle of Endor. Madine was tasked with finding a way to destroy the shield generator protecting the second Death Star. His personally-trained soldiers captured the Imperial shuttle, Tydirium. With this shuttle, Madine's troops, under the command of General Solo, infiltrated Imperial territory on the Sanctuary Moon.
Madine, a Corellian, was formerly the leader of the Storm Commandos, an elite Imperial army unit. When their missions became increasingly objectionable, Madine abandoned a promising military career to fight for the Alliance.
Photos suggest that sequences of Madine commanding a Rebel star cruiser were filmed, but ultimately cut out of Return of the Jedi.