The career of Sir Thomas Beecham ( 1879 - 1961) is so well-known as to make detailed comment uneccessary.
Suffice it to say that for the best part of 60 years he was one of the most important musicians in the United Kingdom, forming two orchestras that survive to this day (the London Philharmonic & Royal Philharmonic), and leaving a great legacy of recordings from the acoustic era through to the age of stereo.
He introduced artists such as Chaliapin to the British opera-goer, and gave the UK premieres of Strauss' modernist operas Salome & Elektra.
Although he presented himself as a gifted amateur, he was in fact a musician of the highest order, who studied each piece in great detail & often committed it to memory.
He could be high-handed, for example in his "improvements" to some pieces, but there can be no doubting his huge contibution to music.