 Pat Tillman, motivated by the September 11, 2001, terrorist attacks, joined the military and walked away from a $3.6 million contract with the National Football Leagues Arizona Cardinals. But Tillman gave up much more than that. On April 22, 2004, he was killed during an ambush attack in Afghanistan while serving as part of the 75th Ranger Regiment, an elite special-operations force of the United States Army. The Army, one month after his death, said he was probably killed by "friendly fire," or gunfire from his own unit.