Thorn, Matfield and O'Connell are three magnificent locks who produced an extensive list of top-grade performances at the highest level. When players of that calibre quit, it is appropriate they get high levels of acclaim.
Matfield is the lineout king whose speed across the ground and in the air make him a rich source of possession. His tactical flair keeps him ahead of most rivals and his athleticism has kept pace with the rising tempo of test rugby.
Thorn brought relentless power and unyielding mental force to all his rugby.
With Ireland and the Lions, who he captained, O'Connell combined the finesse and the swagger needed to reach a century of caps for his country while his charismatic leadership added another layer in those teams' arsenal.
Wallaby captain John Eales was a magnificent athlete and thinker of the game, an erudite leader who was part of two World Cup triumphs.
Fabien Pelous was a pillar of consistency for the Tricolors; Martin Johnson, the rock in the England pack.
Others in the mix of best locks in the professional era would be All Black Ali Williams whose lineout and all-round game was at a peak about 2005 and the craggy Bakkies Botha who used to provide the Springbok muscle alongside Matfield.
Don't ignore Brodie Retallick or Sam Whitelock either. At 24, Retallick has already been the world player of the year and the 26-year-old Whitelock has produced an array of quality work during his 60 caps.