Jimmy Wilde (1892-1969) of Tylorstown, Rhondda, was the first officially recognised World Flyweight Champion. Wilde appeared small and weak in stature, but possessed the combination of a fierce punch and perfect timing. Nicknamed 'The Mighty Atom', he won 101 professional fights over the course of four years and is regarded as the greatest Flyweight boxer of all time.
He became World Flyweight Champion after defeating the American Young Zulu Kid on 18 December 1916.
Named after Hugh Lowther, 5th Earl of Lonsdale, patron of the National Sporting Club, the Lonsdale belt is awarded to British boxing champions. From 1929 they were awarded by the British Boxing Board of Control and champions who win three title fights in a division are allowed to keep the belt.
Source
Encyclopedia Britannica