He trained Rambo personally and commanded him in Vietnam, meaning they have a very strong bond.
As the film ends, Trautman convinces Rambo not to kill Sheriff Teasle, the man who is at the forefront of tracking him down and even listens to Rambo’s trauma, persuading the soldier to surrender.
In the novel, however, this is very different.
In fact, the pair never even meet in the book, and Rambo only ever heard Trautman’s voice over the loudspeaker at his training camp.
The novel ends with both Rambo and Teasle’s deaths, and it is Colonel Trautman who shoots Rambo as a mercy killing, while he is already fatally wounded.