Tony Soprano heads down the psycho path

It's a signature of "The Sopranos" to mark each season with a particularly gaudy psychopath, one over-the-top individual completely unable to control his or her rage, a murderous crank who represents the unromanticized side of mobster life.

Livia Soprano was the show's premiere nut job, a blackly comic monster who put the lie to the myth of maternal nurturance by conspiring to eliminate her son. Next up was Richie Aprile, the polyester wonder who had his "Manson lamps" aimed directly at Tony's job before they were put out. Ralph Cifaretto, even more hot-headed and irritable under his toupee than Richie, picked up the mantle last season, his fatal abuse of a stripper the bloodiest of his many brutal acts.

But the deepest, darkest theme in the fourth season of "The Sopranos" has been Tony Soprano's shift into that role usually reserved for others. While the 12 episodes so far have been in narrative disarray, flawed by an inordinate number of plot lags, loose ends, and character inconsistencies, the animalization of Tony has lent them a powerful sense of unity. The season wraps tonight at 9 on HBO with a 75-minute episode, which was not available to the press for preview.

Tony has always been ruthless and rageful, of course, like his mother but also in reaction to her. But his violent activity has generally followed deliberation or a flash of business savvy. He has been the reliable figure in a population of shaky leaders (Uncle Junior), borderline girlfriends (Gloria), and small-minded captains (Paulie), and not one to jeopardize his own survival and ascension with sloppy behavior. His identity as both a murderer and a careful middle manager and family man has made him one of TV's most morally confusing characters.

But the "impulse control" issues he has discussed with his psychiatrist, Dr. Melfi, have come to a head this season, culminating in his impulsive farewell to Melfi two weeks ago. One of the most stunningly raw moments of the season - if not of the entire series - was the image of an impassioned Tony pulling off his belt and whipping the half-naked Assemblyman Zellman in his own bedroom. Tony descended to an almost primitive state, like a caveman swinging his club at an enemy who had taken one of his female possessions. If David Chase hadn't already used Nick Cave's "The Beast in Me" on the show's soundtrack, it would have been a perfect fit at that moment.

Tony's murder of Ralphie was also the result of impulse. Unlike the murder of Pussy in season two, this was personally motivated, and it may cause professional trouble if it further undermines his already weakened crew.

Coincidentally, as Tony has become more animalistic, his emotional connection to animals has heightened. His tenderness for animals has been in evidence since the first episode of "The Sopranos," as he communed with the ducks in his backyard. This season he sank into despair and hatred after the death of racehorse Pie-O-My, a direct contradiction to the horse-killing-mobster reputation made famous in "The Godfather." His connection to animals - he even yelled at Christopher for killing Adriana's dog - goes against the common thinking about psychopaths, and the inconsistency only makes him a more compelling character.

This season, as Tony has taken over as resident psycho, the tone of the show has become less humorous. There have been sharply comic moments, particularly with Paulie's mother, an amusing creation with her clapper and her elderly gullibility. Paulie's attempt to erase Tony from the portrait of Pie-O-My was a kick, and so was the Columbia University dinner conversation about "Billy Budd" and gay metaphor. Uncle Junior's unhappiness with the courtroom sketch of him, and his subsequent leer at the sketch artist, were classic. And so was the moment Tony realized that Carmela was raiding his cash stash. But most of those bits were overshadowed by somber events - Gloria's suicide, for example, or Paulie's desperate murder of his mother's friend. They have made season four of "The Sopranos" its darkest yet.

And so the portrait of Tony Soprano continues to deepen, making him arguably TV's most intimately known character ever. The only other "Sopranos" character to become more complicated this season has been Adriana. Until she was forcibly turned by the FBI, she was one of the show's more limited presences, a one-joke supporting player despite actress Drea de Matteo's ability to milk the bimbo New Jersey accent for all it's worth. Now she's more dimensional, having had some of the best scenes this season as her desire to blithely trust has been poisoned forever. Clearly, de Matteo can play drama and comedy.

Otherwise, too many of the "Sopranos" characters have been in a holding pattern, particularly Carmela. The show's writers usually keep their plots lean, expecting viewers to pay close attention rather than restating points for those who had their brains on pause. But the flirtation between Carmela and Furio has moved at daytime-soap pace, with each week bringing some new eye contact or interrupted moment between them. Perhaps the pace reflects the writers' reticence about the story line, some awareness of the unlikelihood of a serious attraction between the two characters. They may be thinking that the affair will seem less peculiar to viewers if it unfolds very slowly.

Will Furio and Carmela provide the climax for tonight's finale, now that Carmela is disaffected from Meadow and has enough money to flee to be with Furio? After the Zellman whipping, we know that the thought of another man with one of his women is unbearable to Tony. Will he go after them in his raw state? "The Sopranos" has had its weakest season so far, but it still contains plenty of its most important ingredient: unpredictability.