Valeera has been present in WoW at many times over the years. She originated from the comics/books, and was a slave/gladiator same as Varian and fought on his team while he was missing.
She's been present in a lot of the big patches hanging around other notable alliance figures beside varian at times.
She's also present a lot in Legion in the Rogue class hall chain and is a rogue champion.
She is effectively the game's "face of rogues" the same way Chen is for monks, or Malfurion is for druids.
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Peeps also talking about such boring characters here.... Leah? The chick that's only notable for being Deckard Cain's relative, and all she does in D3 is follow you, worry about her uncle, then die. This is why so many of the characters, even main ones, from other franchises are not being used - they're not "epic" in the manner that Blizzard defines. Leah may have been a main character but she was a useless plot device with almost no character or background, was not heroic or epic or even interesting in any manner. Terrible choice to cite for other franchises.
WoW characters on the other hand are almost always more fleshed out and combat-oriented to begin with, and are well suited to Heroes.
Even a standard, dime-a-dozen Siege Tank unit from Sc2 is more interesting and epic than Leah and justifies becoming a hero (sgt hammer) more than her.