Complex sentence: Tom Johnson (c.1750--1797), born Tom Jackling, was a bare-knuckle fighter who was referred to as the Champion of England between 1784 and 1791.
Split into simpler sentences: Tom Johnson (c.1750--1797), born Tom Jackling, was a bare-knuckle fighter of the 18th century in England. He was Champion of England between 1784 and 1791.