Fred adopted Vegas several years ago. Before getting him, back when Archie was merely a child, Fred told Archie that it would be his responsibility to take care of the dog, especially when he's sick, ensuring that he had food and water. Since then, Vegas has become Fred's responsibility more than Archie's.
Vegas is seen for the first time when Archie is running late for his first day of school. Vegas is seen running after his owner, curious as to what is going on and happy to see Archie. Vegas jumps up at Archie's legs, and Archie, despite being late, takes a moment to pet his dog before leaving. Vegas barks at him as he leaves, and then sits next to Fred.
Fred feeds Vegas bacon as Archie comes down for school. He stood near the stove, looking up to the food being prepared as Fred and Archie discussed Archie's habit of sneaking out in the night, which Fred has been aware of since Archie was eight, when he was sneaking out to Jughead's treehouse.
Archie told Sheriff Keller and Mr. Weatherbee that on July 4th, he was down at Sweetwater River with Vegas, writing songs, when he heard a gunshot. However, this was merely a story that he spun in order to protect his relationship with Geraldine Grundy. As Archie returned home from football practice that evening, Vegas greeted him. He jumped all over Archie as he proceeded to rub him.
Vegas sat in the garage alongside Jughead, who rubbed his head, as a party took place just within the house. They were soon joined by Archie, who was concerned with the arrival of Valerie, his ex-girlfriend.
Cutest Origin Story Ever
After Archie came home from the hospital with Veronica, he was greeted by Vegas. As Archie took Vegas for a walk together with Veronica, he tells her the story as to when his father got Vegas. When he was a little boy, before they got Vegas, his father told him that Vegas was going to be his dog and his responsibility. His father asked him if he was "ready to walk him, give him his food, fill his water bowl, take care of him when he gets sick." As he told her that he wanted Vegas so bad, that he was like, "Yes, Dad, I'm ready. I'm so ready." Veronica confesses that it's the "cutest origin story ever." She then asked him what else. Archie replied that "now, when I get home late from football practice...my dad's already walked him. Saturday mornings, dad takes him out so I can sleep in. Every time Vegas gets sick, Dad always goes with us to the vet." The truth was that no else loved Vegas more than his own father does.
When Archie went over the border to lay low and work at a forest lookout, Fred gave Vegas to him after they had met. 
He stayed by Archie's side as he got attacked by a bear and warned him when dangers appeared.