Tom Sizemore starred as Col. McKnight in Black Hawk Down. To prepare for the role, in addition to reading the book on which the movie is based and listening to the team of advisers, he phoned up the Colonel himself a few times. 

Tom Sizemore

Col. Danny McKnight

But he acknowledges that what helped him most were all the comments of the Rangers who served under the Colonel, things like:

"No matter what you were doing, he was always there, in the streets, with you, beside you, fighting and leading his men."