Conversation so far:
when did the old £50 note go out of circulation
By the end of 30 April the old-style £50 banknote featuring the image of Sir John Houblon is being withdrawn from circulation by the Bank of England.
Who is the man in the banknote of the £50  in England
Sir John Houblon was the Bank's first governor. His image was replaced on the new note with Matthew Boulton and James Watt.

Question: Who are the men that replaced the old one
Self-contained rewrite: Who are the men that replaced John Houblon in England's £50  note