Christopher Moltisanti is technically Tony Soprano’s cousin, but because of their age difference, Tony refers to him as his nephew. Christopher is a hothead with a smart mouth, but he’s intensely loyal to Tony. In fact, part of Tony’s long-term plan is to move Christopher up the ranks of his crew into a leadership position and distance himself yet again from his operation. Christopher was often trusted to clean up Tony’s corpse-related messes, which takes a mental toll and likely contributes to his drug habit (more on that later).
Christopher seems to have it all: a career path, youth, good looks, and a beautiful fiancée in Adriana La Cerva. Sure, he’s a little impatient and frequently flies off the handle, sure, but what mobster doesn’t have anger issues? His real problem, though, is his heroin addiction, which makes him a liability for Tony. Tony helps Christopher get into rehab, and for a time, Christopher seems to be on the wagon again. Tony entices him to start drinking again in the mistaken belief that it is the lesser evil of two addictions, starting him down a dark path. When Adriana tells Christopher she’s an informant for the FBI, Christopher is loyal enough to tell Tony, who has her killed. Christopher goes back to heroin, even as he finds a new woman to marry and have a kid with.
When he crashes a car he was driving with Tony in it, he begs Tony to take the fall because he’d fail a drug test. In one of the show’s most shocking scenes, Tony’s response to his irresponsibility is to asphyxiate him and cover it up.