He leaves us in stitches.

Introduced as a limited-run character during Buffy's second season, Spike thrills us with his domineering, venom-dripping cockiness, and his menacing way of delivering punchlines to accompany punches.

He makes us laugh.

So good at being bad was he that Buffy's creator/producer/writer/director/ dishwasher Joss Whedon made him a regular.

"We knew we wanted to bring him back because he's funny, he's dead-on, he's got a good, sexy menace but at the same time can play the humor," Whedon said. "And that character tracked so well with everyone else, when we brought him back (last season), it was just clear that every time this guy's in the room with someone he puts a different spin on something."

This season, Buffy's fourth, the wiley Whedon has put a nice-guy curse on Spike. No longer can he harm the good guys -- Buffy, Willow, Giles and the rest -- thanks to an implant imbedded in his body by a demon-battling government project called the Initiative. In fact, he has to rely on them for protection and sustenance -- and, in turn, has sometimes been forced to make do with good-guy things, like clothes. Spike in Hawaiian shirts and plaid shorts is Spike in misery.

Recently, Spike learned he still has the capacity to hurt -- but only creatures of his naughty ilk. For Spike, the day he learned he could inflict pain was the equivalent of a millennium New Year's and a 250th birthday combined.

"Let's kick some demon (tail)!" said he.

And we laughed.

The man behind the man known formally as William the Bloody (for his talent of maiming victims with railroad spikes) is 30 years old (though he prefers to say 28) and -- what's this? -- a Shakespeare enthusiast who once portrayed Jesus in a theatrical production of Godspell.

"I've always been an actor-in-waiting," James Marsters said.

Marsters says he's been calling himself an actor-in-waiting since the fourth grade, when he had the role of Eeyore in a production of Winnie the Pooh.

He bounced from his native California to New York City to Chicago to Seattle before landing Spike -- and "bounce" should be taken literally. He apparently has had a rough-and-tumble past, something he wasn't willing to get into during a recent conversation.

Asked if, like Spike, he was born to bruise, he said, "Well, yeah, but I'm trying to do a little less of that these days. That was back in my wild days. I'm a lot happier now."

The "wild days" was the New York period, when he was a bartender and "hung out with the wrong people and did the wrong things. Most of the people I ended up hurting probably deserved it, so I don't have a lot of guilt, but I'm glad I made it through without too many scars."

In New York, he found trouble but not a lot of work.

"No, none, zero, goose egg. It was pretty brutal for me."

So he moved to Chicago and landed a job as Ferdinand in The Tempest. The man is crazy for Shakespeare.

"He's the bawdiest, dirtiest, most violent playwright ever," said Marsters, who says he's acted 10 or 12 parts written by the Bard. "He goes straight for the jugular. We tend to think of him as artful and high class, and it's all so not true. The guy wrote from the gutter, but he also was able to talk about everything from the visceral to the most transcendent."

His fave: Macbeth. "It's a very mature rumination on evil, which is apropos to our conversation."

After a two-year stint as a theatrical producer in Seattle ("I got tired of the Chicago weather"), he moved to Los Angeles. Buffy came six months later.

"It was very lucky on my part," he said. "Spike was originally envisioned as the ornament for Drusilla. I was her boy toy. Or I guess her girl toy. ... I expected to die in three to five episodes. but they didn't kill me; they put me in a wheelchair for half a season. So I'm still here."

He does not know why he's lucky enough to still be on the show.

"I have never looked that gift horse in the mouth," Marsters said. "I always say it's because the haircut worked. They gave me a cool long coat, and that worked. I would guess it's because I didn't (mess) up too badly."

Whedon, in a separate conversation, spoke up for him.

"He's enormously popular," the boss said. "He's such a fun, larger-than-life character. He's so excited to be there. He loves the craft. He spills out that joy of the work that's so infectious and fun to see. He's the best bad boy."

The best bad boy, like other Buffy characters, shows up now and then on the Buffy spin-off series Angel.

"For me personally, I like to show up on the set more when I know I'm going to kick butt," Marsters said. "The fun thing for me is the fight scenes. You get in a fight, and nobody really gets hurt, and nobody gets arrested. It's great. We all pat each other."

So how long is his power going to be limited?

"I haven't been given any clues," he said. "As a fan, I would think that's probably a very good way to achieve the only thing to do, to make Spike into a character you can keep around indefinitely."

Marsters' contract takes him through another season. On Friday, both Buffy and Angel were renewed for a fifth season.

During his down time, he loves to tool around in his 1965 Mustang.

"Actually, it's not mine, it's my girlfriend's," Marsters said. The bad boy's best girl is actress Liz Stauber (Three Kings). "I bought it for her Valentine's Day last year."

Any rumors of a spin-off starring Spike?

"No, but you can start some," he said. "I think it would take a herculean effort to design a show that Spike could be the lead. We can teach our kids, This is where the jugular is."