I've seen quite a few wiki pages for historical figures which include an external link to their WIkipedia page and I just wanted to know if it's mandatory to add it when making a wiki page for real people.
Not mandatory, but it helps to direct users interested in knowing more about them to go read their wikipedia page, as Danbooru's wikis are primarily for things that would be relevant to tagging, not full biographies
Also, you can add the relevant link for anime characters too. Like fandom wiki, or official site link . This help others user to know those character better.
