Micky Conway - tragic story but in 1972 he became our youngest ever scorer. A record taken off of him by another oft mentioned on this thread, Jake Robinson
Not a player who didn’t cut it, but I genuinely believe one more season with us to develop before moving to the prem would have seen him as a regular international and even more of a hero than he turned out to be. These days he would have been taken by a top club and loaned back to the championship to develop further.