Who was the best defensive player in NBA history?

Probably Bill Russell. The man was so intimidating on defense that opposing teams would settle for low percentage shots farther and farther from the basket because they knew Russell was waiting in the interior waiting to block any shots near the rim. The guy would have averaged 10+ blocks a game had they been counted back then and numerous DPOY awards..

BTW if anyone is interested I can give a list of the best defensive players by the decade my votes are:
1960s: Bill Russell, Wilt Chamberlain, Jerry West

1970s: Walt Frazier, Kareem Abdul Jabbar, John Havlicek

1980s: Bobby Jones, Joe Dumars, Sidney Moncrief, Alvin Robertson, Michael Cooper

1990s: David Robinson, Hakeem Olajuwon, Dikembe Mutombo, Dennis Rodman, Scottie Pippen, Gary Payton, Michael Jordan, Alonzo Mourning

2000s: Dwight Howard, Ben Wallace, Tim Duncan, Kevin Garnett

2010s: Kawhi Leonard, Draymond Green

The 90s really had a lot…

Top 20 greatest defensive players of all time
1. Bill Russell (4x rebounding leader, 1x All-D 1st team)
2. Wilt Chamberlain (11x rebounding leader, 2x All-D 1st team)
3. Hakeem Olajuwon (2x rebounding leader, 3x blocks leader, 2x DPOY, 5x All-D 1st team)
4. Dikembe Mutombo (2x rebounding leader, 3x blocks leader, 4x DPOY, 3x All-D 1st team)
5. Nate Thurmond (2x All-D 1st team)
6. Ben Wallace (2x rebounding leader, 1x blocks leader, 4x DPOY, 5x All-D 1st team)
7. David Robinson (1x rebounding leader, 1x blocks leader, 1x DPOY, 4x All-D 1st team)
8. Kevin Garnett (4x rebounding leader, 1x DPOY, 9x All-D 1st team)
9. Dennis Rodman (7x rebounding leader, 2x DPOY, 7x All-D 1st team)
10. Scottie Pippen (1x steals leader, 8x All-D 1st team)
11. Michael Jordan (3x steals leader, 1x DPOY, 9x All-D 1st team)
12. Dwight Howard (5x rebounding leader, 2x blocks leader, 3x DPOY, 4x All-D 1st team)
13. Gary Payton (1x steals leader, 1x DPOY, 9x All-D 1st team)
14. Sidney Moncrief (2x DPOY, 4x All-D 1st team)
15. Tim Duncan (8x All-D 1st team)
16. Walt Frazier (7x All-D 1st team)
17. Kawhi Leonard (1x steals leader, 2x DPOY, 3x All-D 1st team)
18. Bobby Jones (8x All-D 1st team)
19. Mark Eaton (4x blocks leader, 2x DPOY, 3x All-D 1st team)
20. Kareem Abdul-Jabbar (1x rebounding leader, 4x blocks leader, 5x All-D 1st team)