Oscar Robertson willed teams to 10 playoff appearances in his 14-year career. Walter Ioos Jr./NBAE via Getty Images

One of the most indefinable but oft-used words in pro basketball is intimidation. Championships are seldom won solely because a team has an intimidator (unless that player also happens to be a great player), but it can be argued that some teams haven't gone far enough because they don't have one.

The subject comes to mind as the Houston Rockets, mired in mediocrity, play tonight in Orlando against the Magic. The Rockets have two of the most potentially intimidating players in the league -- 7-foot-6 center Yao Ming because of his size and 6-9 Tracy McGrady because of his myriad talents. Yet neither is an intimidator, Yao because he is naturally self-effacing and uncomfortable playing a physical game, McGrady because he tends to settle for perimeter shots and seems to take losing a little too comfortably. Still, both are great guys to be around and the fact that they are not intimidators should not define them as human beings. San Antonio's Tim Duncan, arguably the league's best player, is not an intimidator either, but his supply of talent is so abundant that he doesn't need to be.

Anyway, the tonight's game got me thinking, for this week's five pack, about the five greatest intimidators in NBA history. I'll be the first to admit that the definition is hazy. Shot-blocking, for example, is the clearest way for a player to demonstrate that he's an intimidator, yet I would put neither Dikembe Mutombo nor Mark Eaton on my list of all-time intimidators. It takes something else, something indefinable.

So here we go.

Bill Russell of the Boston Celtics

He was the first great intimidator even though he played in an era when blocked shots were not even kept by statisticians. Russell wasn't as great an offensive player as George Mikan, who preceded him, or as devastating an all-around force as Wilt Chamberlain, who came into the league three years after him, but when teams went up against Russell, he had an aura of invincibility about him. He was going to block your shot from in front, he was going to catch up to you and block your shot from behind, he was going to make an outlet pass, or finish a fast break, or knock you on your butt or do something to beat you. But he was going to beat you. As great as they were, I don't think Mikan or Wilt had that quality.

Oscar Robertson of the Cincinnati Royals and Milwaukee Bucks

One of the most interesting basketball conversations I ever had was with Jerry West about The Big O. They are eternally linked as the quintessential all-purpose guards of the NBA's first 25 years, but don't try to tell West that. "I never felt that anybody -- anybody -- ever played the game better than Oscar," said West. "You just always felt he would find a way to beat you."

Robertson played physical, he played smart, he played tough. Moreover, he had that cold-blooded tyrant aspect to him (as did Russell). Even his teammates were a little scared of him. I always argue that Magic Johnson, for my money, was a better player than Robertson, simply because of his size (they both played point guard and Magic was at least three inches taller) and because Magic represented the next step in the evolutionary chain. But as an intimidator, I'll take the grim-faced Robertson over the smiling Magic. (If you're talking about which one you'd rather spend a few hours with, that's a different question with a different answer.)

Kareem Abdul-Jabbar of the Bucks and Los Angeles Lakers

Unfortunately, many remember Kareem in his later years with the Lakers, when he was still a terrific offensive player but was propped up by the overall brilliance of Magic and the willingness of teammates such as Kurt Rambis and A.C. Green to do the grunt work. But don't ever think this guy wasn't an intimidator. He wasn't exactly the emotional descendent or Russell or Robertson; rather than being a gnarly caustic type, Abdul-Jabbar had about him the air of mystery. It began way back in high school when he, perhaps America's first storied scholastic player, took his talents 3,000 miles West to UCLA, listened to jazz, bonded with John Wooden and never let the public get a true glimpse of him. Russell would explode from time to time and Robertson wore his disenchantment with society (and the guys he was playing against) on his face. But Kareem, for the most part, wore a stoic mask.

But everybody in the league knew that he could get two points on you whenever he damn well pleased. Throw the ball into him and let him get into his sky-hook rhythm, and it was pretty much all over.

Larry Bird of the Boston Celtics

Why Bird and not Magic? It's a tough call. But I always thought that Bird grinded his way to success more than Magic and dominated by the force of his will as much as by his talents. That doesn't mean that Magic wasn't tough and that Bird didn't have athletic ability. It just means that Bird was slightly more intimidating.

Larry Bird's confidence was reflected in the play and success of his Celtics teammates. Andrew D. Bernstein/NBAE/Getty Images

By nature, Bird was more like Robertson that the other aforementioned two. He didn't have that Russell anger or that Abdul-Jabbar mystery. Given his own devices, he would've rather just laced 'em up, put a beating on somebody, gone home, gotten up the next day and done the same thing. But he played in an era when Madison Avenue got interested in the NBA and so, to an extent, he became an icon, even an amiable media presence.

But if there was one thing you noticed around the Celtics in the Bird Era was the mood change that enveloped the whole team when Bird was angry or dissatisfied with his teammates. "I'd like to talk to you," a Celtic told me one time, "but Larry thinks we've been giving too many interviews and I don't want him to see me."

To his opponents, Bird was an inveterate trash-talker. He once pointed to a spot on the floor and told his defender, "That's where I'm going to hit a 3 in your face next time down the floor." He did, too. That's intimidating.

Michael Jordan of the Chicago Bulls

Jordan was the first smiling intimidator. He wasn't angry about social causes, as Russell and Abdul-Jabbar were. He wasn't angry that he didn't get his due as player, as Robertson was. (There were many years when Jordan wasn't happy with his salary, but, since he was making $35 million off the court, he couldn't get too upset.) And Jordan wasn't by nature a tough-minded loner, as Bird was. He realized early that a pleasant disposition would earn him a crossover appeal and millions in endorsements.

But -- and it's a big but -- it was all, to an extent, a façade. Jordan intimidated (sometimes heartlessly) his teammates in practice and tortured his opponents (sometimes joyfully) in equal measure. The most intimidating thing about playing against Jordan was that even though it often appeared he would spend too much pregame time playing golf or gambling or arranging tickets for friends or all of the above ... he was still going to kick your butt.

As much as blocked shots or hard fouls, that's what makes an intimidator.

Sports Illustrated senior writer Jack McCallum covers the NBA for the magazine and is a regular contributor to SI.com.