ADinoSupremacist's board-to-board with Subtank
From Halopedia, the Halo wiki
I would say his first appearance would be in First Strike. But then again, it depends on what is mean by "first appearance". I suggest talking to Jugus or someone who is active in the Appearances project.
You can send it here (the only way for people to contact me). If you don't want others to read your message, mark it as private.
I've set a protection on it that last for a week. Until then, keep it in a notepad or in the talk page of the article.
Also, note that it really doesn't matter who added it first. There is no "first" competition in Halopedia. So, people take credit for saying it first? Does it really matter? Do they actually gain something useful in their life for being first in getting information about a video game out (unless they're doing it for a living, then that's a different story)? It's a bad habit and simply childish/amateurish/immature. Instead, take the better approach by taking the "So, wut?" way.