Reason:
Lich King is a character name, not a subspecies of lich, so it wouldn’t apply for images where the Lich King is a different species or is being cosplayed. For example:
post #1612228

Here's the link

I mean, even in Warcraft he wasn't a Lich, Arthas was a Death Knight... Ner'zhul was the proper Lich king, and Bolvar's still a mystery.

But I instead propose just adding a suffix _(Warcraft) instead, as I had to do for death_knight_(warcraft) because the proper death_knight tag implies undead, something that might not always be seen in Warcraft's version.