"I think he's a leader of an evil organization." All eyed to Max at that declaration. "Think about it, Ash goes around regions aiding legendries, stopping the likes of Team Rocket, Magma, Aqua and even though it might cliché Ash's father being apart of an organization like Rocket or Magma would work." With a stratified nod Max rested his case.
"Max just because Ash foils Team Rocket, Magma, Aqua, etc… doesn't mean his father is leading a criminal organization." Misty pointed out.
"Yes it does because it would be fittingly ironic." At Paul's raised eyebrow the boy continued, "Think about it Ash ends up saving the world so irony would dictate that his father is trying to conquer it."
"Max…no just no," May couldn't help shake her head, "Clearly Ash's dad has an out of town job, possibly out of region, and he sends money to his family. It would explain why he's never around when we've stopped by and how they are able to afford their place since I don't think Mrs. Ketchum has a job."
"But that's boring," and before Max and May could get into it Misty's voice cut in with a one word, "Wanderlust." At twin looks of confusion turned toward her Misty explained, "Think about it. Ash is always traveling the region and never staying in one place for and his mom is able to reside in Pallet Town without a problem, so clearly he had to have inherited from somewhere."
"I don't know. It could work but I don't think wanderlust is hereditary. Besides if your theories were true than Ash would have at least talked about his dad in some way. Therefore my theory is that they have a strained relationship, and just don't really talk much." Dawn concluded.
"How did our conversation go from catching up to Ash's deadbeat dad, again?" Paul couldn't help but ask. "Oh come on," he responded to the looks, "while no one said anything it was clear that Mr. Ketchum wasn't around it. So it's obvious the guy just left his family one day, to never return."
"No he leftfor his evil organization plans."
"You mean out of town work to support his family."
"If he really needed work to support his family, Professor Oak would have helped him get a job. So clearly the answer is wanderlust."
"I'm pretty sure that Mrs. Ketchum works or owns a restaurant, so they have a strained relationship and that why Ash's doesn't mention him."
Paul couldn't help but snort as he replied, "Or he doesn't mention him since his dad couldn't handle being a father and left his family."
As the five began to continue their argument at Misty's place (Max and Paul doing a journey through Kanto for badges and May and Dawn trying out the new coordinator circuit), Ash and Brock travel through the mysterious Kanvo* region.
Author's Note: Edited as of 3/24/2016 for clarity on Max's position and revised the author's note somewhat.
Also my own theory is that Ash's father died when he was young and there's a tactic acknowledge that Ash doesn't bring him up unless his mom does first. But I couldn't fit in here in why that I liked. Furthermore Ash and Brock are mentioned at the end because I wanted to include them in some way but couldn't fit them in with the group tossing their theories.
*Combination of Kanto and Unova, because why not.