Born in Ponyville after Fluttershy turned it into a Hellhound Sanctuary, Romt was raised on the knowledge necessary to help him be one of the Hellhounds of his generation to be more accepting of pony-kind. The history of the Diamond Dog's did not mean as much now, as if anypony in the wastes wanted to thrive, they needed cooperation. Romt generally never showed any distrust towards the caravan ponies that visited the Sanctuary, being more equal and friendly with them as planned by the elders. The pups were certainly going to be a step in the right direction for Equestria.
Over the course of his younger years, he was taught effective techniques used by the Hellhounds; Digging techniques were considered necessary, and a focus on strength and agility was also necessary to ensure a Hellhound was still at odds of winning a fight without a gun. Though he did have firearms training, but never got the chance to use much in the way of Energy Weapons due to them becoming rarer. A part of his firearms training was learning how to modify weapons so he could hold and fire them in his hands. The process wasn't half as complicated as it first appeared for him, and after being given time, he learned how to modify weapons without wasting too much precious time. It wasn't an instant process, but it was fast enough to not take up half his day.
What time was left after training with the older hounds, he mostly spent with other pups like himself. They enjoyed a bit of play, and listening to stories on the radio about events before their time. They also practiced with each-other in a competitive fashion. Romt was the second strongest pup, but forth fastest mechanic out of the six of them. He tended to slip up at times, prolonging the process of modifying guns. As irritating as it was, he was usually just told that slip-ups happened when trying to do work quickly. Which, while true, didn't make him feel much better.
As he began to grow older, Romt began going out to patrol the caravan routes with the elder hounds. This was a task Hellhounds were generally good at, as they could cover a lot of ground and deal with issues more effectively than Earth Ponies and Unicorns, and could compete fairly with pegasi and Griffons for the most part. His first encounter with an enemy came during his second run; He and his leader at the time, Gurzil, encountered a small group of raiders waiting to ambush a caravan. He proved to be fairly competent; Taking out one pony with a shot to the neck, and also landing a shot to the chest of another. There was the occasional miss during the firefight, but overall Romt didn't waste too many bullets to make himself concerned. He felt satisfied with getting through without being injured, though Gurzil ended up being shot in the arm, which was certainly concerning for Romt. The bullet passed through, but it halted them until they stopped the bleeding.
Patrols of the caravan routes would continue for years, it was becoming his job to ensure trouble was cleared away for the caravans so they could pass through. Some thoughts crossed his mind as he got older, mostly about how closed in he felt with just trotting the roads. There were enough taking to the roads, weren't there? He wished he could have some more freedom rather than this task that many others were doing. He figured that trouble had to run out in the wastes as well. so having him out there could help more ponies than just the ones travelling the caravan routes.
The best decision he could make was to bring it up with the elder hounds for their opinion on the matter, and their response was simple; He could leave to travel the wastes how he liked, but would be on his own. He could always return, but it'd be generally more dangerous to explore off the roads, leading to him being unable to make it back. Not caring too much about the conditions, he stated he would be leaving to patrol more than just the caravan routes, and provide assistance to others who needed it. This decision was respected by the elder hounds, and soon after their discussion, he had collected basic supplies and left without much more thought. He wasn't sure where he was heading, but had a basic idea of where areas of interest were.
He traveled a fair distance, occasionally visiting towns for supplies, but sometimes having a difficult time interacting with them. Over time, his visits to stores became more common and he was more welcomed, but at first it was mildly rough for him. This stood for his journey as well; He had some difficult times in the wastes, sometimes hardly able to afford supplies, or having to deal with the Equestrian Wasteland's many dangers that didn't even involve right or wrong. Then there was the times right or wrong was thrown into the mix, making his life harder as he tried to uphold the peace and keep those who were innocent safe, which involved risking his life on multiple occasions.
As of now, he's grown to be a sort of helpful figure for the wastes. He's not exactly well-known, but ponies don't tend to forget a mutt like him once he lends them his aid. Deciding to travel a caravan route for old time's sake, he met a small group being assaulted by the remains of a raider squad. Between him and the caravan guard, the raiders were dispatched without much harm to the group or the caravan goods. After taking a moment to recall good memories of his time as a growing pup, and a minor introduction to one-another, Romt decided to travel with them to New Appleloosa giving he was running short on supplies. He'd be there for a short while to make sure he was prepared to hit the trails once again, where nopony could ever be sure of what would happen next.
Added a few things more for my own amusement, but there's my character.