Think about it. Assume that the comic takes place in 2009. Kahn mentions that Gary disappeared ten years prior. The date on Ash's statue? 1981 - 1999. 1999 being 10 years before the comic, the same year of the other's disappearance. The two incidents are probably related.
Not sure of his motivation exactly, but basically he roams the land now punishing other 'Gary Oaks', seeing as how he does specifically go after Atty who he identifies as a Gary Oak, even with a speech about justice.
Could possibly be as atonement for being the original example of it, if coupled with the above WMG then this could be triggered by Ash's mysterious death.
- Alternatively . . .
If the disappearances are connected, then it may be possible that both bodies were never found. It's just assumed that both are dead. However, it may turn out that Gary really did die, and Ash is so consumed by guilt at failing to save him that he could never bring himself to return home (out of shame and out of fear of confronting Prof. Oak about what happened). He's spent the last ten years taking his anger and frustration out on whoever he deems to be an abusive trainer: trainers who couldn't care less about their Pokémon, who only want to use them for fighting, and who purposely target weakened or helpless trainers. Unfortunately, years of bitterness have hardened him to the point where he's not above completely devastating the Pokemon of Jerkass trainers.
As for where Pikachu could be in all of this . . . maybe Ash lost him, too?
Unless the Gym leader has changed, Atticus will face Brock, who happens to be one of Ash's closest and oldest friends. There might a possibility that he could end up hinting at what happened with Ash and possibly Gary.
- Assuming this is actually in the anime universe and not just naming Red and Blue Ash and Gary, then Brock's brother Forrest is the Gym Leader.
- The Gym leader is revealed to be a blonde chick named Elle. It remains to be seen if she will answer any questions.
- Elle turned out not to be the leader after all.
- The artist cares little about the lore, but there may be a bigger secret somewhere. Either was, a blind dude Jeremy Stein was the gym leader. Doesn't seem to be a recent hire either. Either way, it's been 8 years in universe so Brock could've just moved on.
- So far, she is proving to still be very loyal. She even hit George in Chpt. 8 when she suggested that Atticus doesn't deserve DT.
Also: Black hair.
- It also goes well with the common game WMG about Ash/Red dying after he got beat on Mt. Silver. Gold accidentally pulled a Gary Oak in a dangerous spot and a life was lost because of it, that's why he was so pissed at Atticus.
- So far this is being proven true. Neither Brock nor Bill have appeared in their respective homes/hang-outs (Pewter City Gym and the Lighthouse). Instead they are replaced with Jeremy Stein and Abel respectively. Bill is mentioned by Abel as being the inventor of the storage system, but that's the only time his name is dropped in the comic.