The 1989 film Born on the Fourth of July was an adaptation of Vietnam veteran Ron Kovic’s memoir. It was a deeply personal project for both Kovic and director Oliver Stone. Stone, a Vietnam vet himself, made three movies about the war: Platoon, Born on the Fourth of July, and Heaven and Earth. Tom Cruise, who played Kovic, threw himself into the role to the utmost of his ability.
4. THEY CONSIDERED ACTUALLY PARALYZING TOM CRUISE.
Stone found a nerve agent that would paralyze Cruise for a few days, and Cruise was open to the idea of using it. But the studio's insurance company—spoil sports—nixed it.
5. CRUISE PREPARED BY LIVING IN A WHEELCHAIR FOR A WHILE.
Wanting to relate to Kovic's experience as much as possible, Cruise got himself a wheelchair and role-played for weeks, even staying "in character" when doing media interviews and going to studio meetings. He also accompanied Kovic on public outings to see how a pair of paraplegics were treated. (They were once asked to leave a store because their wheelchairs were leaving marks on the floor.)
Read more about the making of Born on the Fourth of July, not all of it about Cruise, at mental_floss.