Is Tim Duncan the greatest defender in NBA history?

Perhaps the most remarkable statistic of Tim Duncan's Hall of Fame career, which ended when he announced his retirement Monday morning, was this: Duncan never won Defensive Player of the Year.

In fact, despite making the All-Defensive First or Second Team 15 times -- far and away the most since the NBA introduced the All-Defensive teams in 1968-69 -- Duncan never even finished second in the voting for Defensive Player of the Year.

Nonetheless, as Duncan heads into retirement, it's worth pondering whether he's the best defender in NBA history.