Before you read this story it is important to realize that blocked shot stats were not kept before 1974 and therefore the two greatest shot-blockers are not on the list: Bill Russell and Wilt Chamberlain. You can throw in Nate Thurmond too, not to mention Kareem-Abdul Jabbar, whose first four (and most dominant) seasons were played before the stat was kept, which really sucks.
I bet Russell averaged 5 or more a game and Wilt too, but we will never know.
In order for a player to make this list of the 15 greatest shot-blockers in NBA history they had to at least average 1.8 blocks per game for their career and have a blocked shots per minute average of over .070 for their entire career.
These are the greatest shot-blockers of the modern era MINUTE BY MINUTE, which is the most accurate way to calculate it.