Caveman John Raines, left, and Thomas J. Motherway fist bump after crossing the finish line of the 121st Boston Marathon. Photo / Getty Images
By Heath Moore

A nearly naked man nicknamed the "Barefoot Caveman" has stolen the show at the Boston Marathon after completing the event in just bare feet.

Donning only a tan-coloured loincloth, a bone necklace, and just the skin on his feet, 50-year-old John Glen Raines finished the gruelling 42km race in 3 hours, 40 minutes and 43 seconds.

Raines' antics lit up social media when he was photographed crossing the finish line, fist-bumping a fellow runner while in his precariously skimpy outfit.

Despite the presence of wind, the "Barefoot Caveman's" kit remained intact.

It's not Raines' first time donning the loincloth after running his first marathon in the prehistoric getup in 2010.

The 50-year-old is an experienced marathon runner, with records of his feats dating back to 1999.