"Think about the now instead of the what if."
This page contains spoilers from any Gameknight999 book, read at your own risk!
Smithy has not yet appeared in the series, however he has been mentioned several times as a legendary NPC during The Great Zombie Invasion. He first used two swords in Two-Sword Pass. He is expected to appear in The Birth of Herobrine series; in fact, he depicted in all 3 covers. He and Gameknight999 are the only two known Minecraft entities to wield two weapons at once before the 1.9 update that allowed all villagers to make use of both their hands. Gameknight replaced him after he died, which is a secret, only Fencer and Gameknight999 know this.
Even though he died, Smithy plays a important role when Gameknight999 poses as him.
In Gameknight999 vs. Herobrine, Digger and Baker comment on Gameknight999's skills with two swords, saying he fights like he learned from Smithy himself. "Maybe he learned it from me," Gameknight joked, which, at the time, is a very small detail but foreshadows some of the events in the Birth of Herobrine Series. Also in Gameknight999 vs. Herobrine some villagers argue about weather or not Smithy died in two swords pass or the battle that happened afterward. I think one of those The cover of the Great Zombie Invasion might have been foreshadowing Gameknigt999 posing as Smithy. The cover shows them big fighting along side each other, kinda like a mirror.