Here is my list of the Top 10 Greatest Defenders in NBA History:
1) Bill Russell - This only needs one explanation: 11 championship rings. It was his defense that anchored every last one of those 11 titles he won with the Boston Celtics. They didn't keep track of blocks, steals, or even All NBA Defensive teams in his days, until the end of his career where he was on the very first NBA All Defensive First Team in history. He is the proof that defense is what wins championships, and he will always be remembered for that. He will go down as the greatest defender in history.
2) Hakeem Olajuwon - "The Dream" was so good on offense that it made you forget how great his defense was. He was such a good offensive player that people tend to forget the best part of his game was his defense. He was the most athletic center in NBA history and used this too his advantage; most notably being one of only 4 players to record a quadruple-double. He is the 7th all time leader in steals, the highest of any center in history. His defense contributed to two titles for the Rockets. He won the DPOY twice, made 5 NBA All Defensive First teams, and is the only player in history to make the Top 10 in blocks, steals, rebounds, and scoring.
3) Ben Wallace - There has never been a better reason to "Fear the Fro" when Big B was anchoring the great Pistons defense. He made everyone fear coming into the lane and trying to score. He was small in height (6'7"-6'9" not counting the fro), but made up for it with his athleticism and leaping ability. He is probably the 2nd most athletic center in history behind the Dream. He made it to 6 All-NBA Defensive Teams, and won 4 DPOYs (should have been 5, he was robbed by Ron Artest), tied for the most in NBA history. His great defense allowed the Pistons to make 5 straight ECFs, 2 straight NBA Finals, and winning the NBA title in 2004. His defense presence made the Pistons D the best in the league (one of the best all time defense). He is the only player in NBA history to record 1,000 rebounds, 100 blocks, and 100 steals in 4 consecutive seasons. He is also the only player to be able to slow down the great Shaquille O'Neal on a regular basis. If you need proof: http://www.youtube.com/watch?v=fWo-VA1mf6Y
4) Michael Jordan - MJ was not just one of the great scorers of all time; his defense is what made him into the greatest player of all time. We all see the highlights on ESPN of his great dunks, his flashy layups, his great jump shooting, etc., but what you never see is his great defense. For awhile, his haters tried to say he was only a scorer and not a good defender. What does his Airness do in response? Goes and wins the 1988 DPOY that's what. He has made 9 NBA All-Defensive Teams over his career. If you know you're history, the Bulls great defense was their main contribution to their 6 titles and you know MJ was their leader on D as well as on offense.
5) Tim Duncan - Timmy D is truly one of the best post players we've ever seen. His inside presence in the post is not only seen on offense, but on defense as well. He has anchored 4 championship teams now with the Spurs and his post defense is every much a part of it as anything. He doesn't have to put up the flashy defensive stats that many other good defenders do, but if you ever have seen the great defense the Spurs play you will see that it all comes down to Timmy's D. Without him down low, their defense wouldn't be special at all. He has made 11 All-Defensive Teams. The Big Fundamental is a perfect nickname for him because he is better at the fundamentals of basketball than anyone.
6) Dennis Rodman - The dude may have been crazy, possibly even needing to be institutionalized, off the court, but on the court he was one of the greatest defenders this league has ever seen. He started out on the great defensive Detroit Pistons "Bad Boys." He won both is DPOYs with them and helped them achieve two NBA titles with his great defense. He also won 3 titles with Chicago Bulls (along side MJ) playing a huge part in their strong defense. He became known over the entire league as a great defense player, and some even said he "could shut down any opposing player, from point guard to center." He wasn't very tall, but made up for that with athleticism, strength, and leaping ability. For his size, he is one of the best rebounders in history. He was able to average over 18 rpg in back to back season (91-92 to 92-93) as well as averaging over 17 rpg the following year. He finished with 13.1 rpg over his entire career which puts him in the Top 10 all time rebounders per average. He may have been a psycho, but he was a great NBA defensive psycho.
7) Kevin Garnett - KG is the perfect player you'd want to anchor your defense. This wasn't as evident when he was on the Timberwolves (although he was great with them as well), but became even more noticeable when he joined the Boston Celtics last year. Their defense went from an average (middle of the league) defense to the NBA's best defense in 2007-2008. He is such an athletic player that he can be everywhere in the paint playing help defense as well as stopping the toughest post threat for his opponents. His leadership is the key to his game because he is able to motivate and lead his teammates to play much better defense than they would without him. He has so much passion and love for this game, and uses that to motivate himself and his team on defense (as well as offense). He has made 5 All-NBA-Defensive Teams as well as winning his first and only DPOY last season.
8) Kareem Abul-Jabbar - Like Jordan, he is known for being one of the greatest scorers in history, but also like Mike his defense was just as important in helping his team succeed. His made his presence felt in the post on defense making it very hard for teams to get points at the rim. He knew how to use his size to his advantage by using his height and long arms to keep a hand in players’ faces and swat their shot if they dared going up against him. His defense was more noticeable when he was younger (with the Milwaukee Bucks), but he still maintained his great D for his entire career helping to be the anchor of 6 NBA titles. He made 11 NBA All-Defensive First Teams over his career.
9) David Robinson - The Admiral was truly a force to be reckoned with on defense. He was a dominating presence in the post making it very difficult for opposing teams to scoring in the paint. He was great at all aspects of defense: rebounding, blocking, stealing, post defense, etc. You name it, Robinson could do it all. His great defensive efforts won him 8 All-NBA-Defensive Teams, a DPOY, and 2 NBA championships. He wasn't flashy or super athletic, but he commanded respect in the post, and lead his team on defense.
10) Nate Thurmond - The famous "Wilt Stopper" was known throughout history as a great defender. Anyone that could stop the dominating force known as Wilt Chamberlain had to be great. He was tall and used his height advantage over many smaller players to become a great rebounder and defender. Again, most of his career he played in the times before blocks and steals so who knows how many of those he had, but later in his career they counted the stats and he averaged 2.1 bpg in his final 6 seasons. He never won championships or tons of awards (always being left as the odd guy out behind Russell and Wilt), but he was still a great defender that was able to do toe-to-toe with two of the greatest big men the NBA has ever seen.
Honorable Mention: Dikembe Mutombo, Alonzo Mourning, and Sidney Moncreif
Feel free to comment and even make your own list if you wish.