At scienca-revuo.info I just read "Vilhelmo la Konkerinto". Should not he be called "Vilhelmo la Konkeranto"?
This has nothing to do with the question whether William is already dead or still alive, but whether he got the title during or after his deed.
In fact all kinds of participle could be justified:
X-o la Konkeronto (X is devised to conquer something in the future; could be a name given to a new-born child as a blessing)
X-o la Konkeranto (X was either conquering something in the time they acquired the title or, more plausible, was a notorious conqueror, who made this their whole life)
X-o la Konkerinto (X is famous for the conquering (rather than the conquerings) they accomplished)
(Native speakers, please correct my English)
Tio estas regula esprimo. Vd ekzemple: https://eo.wikipedia.org/wiki/Vilhelmo_la_1-a_(Anglio)