By Alex Tresniowski
January 18, 2010 12:00 PM

He’s had enough drama in his life for ten and a half men: getting caught in the Heidi Fleiss hooker scandal in 1995; overdosing on cocaine in ’98; going through an infamously ugly divorce from Denise Richards in ’06. Then came Christmas Day 2009, when Charlie Sheen—the highest-paid actor on TV—allegedly menaced wife Brooke Mueller with a knife and said, “If you tell anybody, I’ll kill you.”

Just 10 days later, Sheen, 44, was back on the set of his hit CBS sitcom Two and a Half Men, which is now filming its seventh season—and for which Sheen hauls in $825,000 an episode. He has, throughout his career, seemed at times to be two very different men: the respected actor and happy dad who beams on his 2009 Christmas card with Mueller and 10-month-old twins Max and Bob, and the haggard figure in his most recent mug shot. He “has a lot of demons,” says Tracy Richman, a dating coach who was his girlfriend in the ’90s. “He always had an addictive personality and he’s been on a roller coaster. There’s a pattern and he doesn’t know how to fix it.”

Yet despite a history of scandal that would derail most actors’ careers, Sheen has stayed in Hollywood’s good graces. In part that’s because whatever happens off-camera, the actor has a sterling work ethic that endears him to his bosses and colleagues on the set. “No entourage, no star trips, just an actor doing his job,” says Two and a Half Men creator and executive producer Chuck Lorre. Says his costar Jon Cryer, who worked with him on Jan. 4: “He’s always incredibly professional, but especially in times of personal crisis. Today was no different.” And, unlike a fallen star such as Tiger Woods, Sheen has never cultivated a straight-laced image. He comes across more like his Two and a Half Men character, an unrepentant cad embraced by fans as a lovable lout. “Charlie never tried to play the good-guy role,” says Richman. “On the show he’s playing who he is.”

Friends say many of Sheen’s troubles have been caused by his problems with addiction, something he has acknowledged publicly. “When Charlie’s sober, he’s sweet, he’s loving, he’s generous, he’s caring,” his former girlfriend and ex-porn star Ginger Lynn Allen told People in 2000. “When he’s drinking and using, he’s out of control.” Sheen has been sober for the past several years, friends say. But the ugly Christmas Day incident seems to have been a relapse. “Charlie let himself down by drinking,” says a friend of the couple’s. “He and his wife had a fight and they both drank.”

Sheen, who wed actress Mueller, 32, in 2008, had just joined her at a vacation home in Aspen when things went wrong in the wee hours of Dec. 25. “My husband had me with a knife,” Mueller said in a 911 call. “I was scared for my life.” According to arresting officer Rick Magnuson, Mueller claimed Sheen pushed her down on the bed, held a switchblade to her throat and said, “I have ex-police I can hire who know how to get the job done, and they won’t leave any trace.” Sheen denied using a knife; he was arrested on second-degree assault and menacing charges, and a restraining order was automatically issued to Mueller. But in the days that followed, Mueller—whose blood alcohol level that night was .13, which is legally drunk in Colorado—hired prominent attorney Yale Galanter to modify the order and help her reconcile with Sheen. “Brooke and Charlie are very passionate about each other and want to try and save their marriage,” says Galanter. “They had a bad night and want to get beyond it.”

The problem is that Sheen has had a lot of bad nights. Many of the women in his life have described the star as a sweet-natured and generous man who periodically falls into dark and even frightening moods. In 1997 he pleaded no contest to a charge of battery with serious bodily injury after his then-girlfriend, model Brittany Ashland, accused him of smashing her face on the kitchen floor. Months after Sheen wed the actress Denise Richards in 2002, he started gambling, abusing prescription drugs and acting in a “very volatile” way, Richards claimed in a 2006 legal declaration. “The smallest thing would set him off.” Richards accused Sheen of spray painting “the dumbest day of my life” on their wedding photo and pushing her around. Their marriage ended in 2006, in the midst of a vicious custody battle over their two daughters.

Sheen proposed to Mueller in ’07, but they hit a rough patch even before getting married. “Today he is acting like you told me he would,” Mueller allegedly said in an e-mail to Richards (the two have been cordial since Mueller’s engagement). “As you know, he lashes out.” Now, their yuletide fracas has again focused attention on Sheen’s antics. At home in L.A. since being released on bail, he has spent time with his daughters while Mueller and the twins are in Aspen. He often calls Colorado and has a nanny hold the phone up to the twins so they can hear his voice. “He wants to be with his kids,” says a pal. “He doesn’t want to get divorced.”

Friends say both Sheen and Mueller want to save their family. But like his sitcom character, Sheen seems stuck in the role of a bad boy who can also be a good guy. “Despite his troubles,” says former girlfriend Richman, “I really believe he genuinely wants to be a better person.”