From Wikipedia:

Frank (Francesco, Francisco) Lentini (May 18, 1881 – September 22, 1966) was born at Rosolini, near Syracuse, Sicily into a family of twelve children, seven sisters and five brothers.

He was born with three legs, two sets of genitals and one rudimentary foot growing from the knee of his third leg. So, in total, he had three legs, four feet, sixteen toes, and two sets of functioning male genitals, which were all that existed of a conjoined twin and jutted from the right side of his body. The doctors determined that since his twin was connected to his spine, removal could have resulted in paralysis. When his parents refused to acknowledge him, his aunt raised him but eventually handed him over to a home for disabled children. As a child Lentini had hated his extra body parts until he spent time at the home. There, he met children who were deaf, blind, and mute. He also learned to walk, ice skate, and jump rope.
At the age of eight, Lentini moved to the U.S. and entered the sideshow business as The Great Lentini, joining the Ringling Brothers Circus act. He gained US citizenship at the age of 30. His career spanned over forty years and he worked with every major circus and sideshow including Barnum and Bailey and Buffalo Bill’s Wild West Show. Lentini was so respected among his peers that he was often simply called “The King”.

In his youth, Lentini used his extraordinary third leg to kick a soccer ball across the stage, hence his show name, the Three-Legged Football Player. By the time he was six, Lentini’s normal legs were slightly different in length–one was 39 inches, the other 38 inches–but the third leg was only 36 inches, and the foot on it was clubbed.[1] Even more as an adult, while his extra leg was several inches shorter than the others, his primary legs were also two different lengths. He was heard to complain that even with three legs, he still didn’t have a pair. He married Theresa Murray, three years younger than him, and they had four children: Josephine, Natale, Frank and James. Frank Lentini died in Jacksonville, Florida on 22 September 1966.

Over on The Human Marvels, there’s a wonderful discussion thread below a photo of Frank in which a number of his descendants/probable descendants have chimed in with questions and reminiscences. It’s well worth a read.