I had assumed this site dealt with factual matters, but since you invite opinions I will submit Tony Benn as a worthy candidate. That's simply because I admire people who are true to their principles, who are wise and intelligent. How many politicians can that be said of?
If he were still alive, Enoch Powell would qualify under similar criteria, so this is not a party political opinion.
Depends what you mean by "great", doesn't it? Mark King is still the greatest bass player alive!