He debuts in the first episode of the first season of and is portrayed by Peter Krause. He was a fire captain in the St. Paul Fire Department until he relocated to Los Angeles and started working as captain of LAFD station after losing his family in the devastating fire that he inadvertently caused.
He is now married to Athena Grant-Nash. Bobby grew up in Minnesota, and is the youngest child of Tim and Ann Nash. He has an older brother named Charlie , with whom he used to play lawn darts when they were kids. His father, also a fire captain, was an alcoholic and had anger issues which were heightened by his drinking. Despite this, Bobby idolized him, viewing him as a hero because of his profession.
At a party honoring his father Tim, Bobby gifted him a scrapbook he had made featuring all the people Tim had saved. During the event, Tim allowed Bobby to take a sip of alcohol, which he immediately threw up. Bobby's mother, Ann, was furious when she found out, but Tim brushed it off, not all that concerned of the consequences. One day, after a big fight with Tim, Ann decided to leave the house, and took Bobby's brother, Charlie, with her.
Bobby refused to leave with them, even after Tim slapped Charlie. One night, Bobby accidentally started a fire while trying to make cookies and there was no fire extinguisher, prompting him to call Tim was furious that Bobby called , as he could potentially get fired due to his alcoholism, not to mention he was also skipping work. In his anger, Tim tossed the scrapbook Bobby had made for him in the trash, which made Bobby hide in his room.
Tim later drunkenly tried to apologize to Bobby, taking the scrapbook out of the trash, but he tripped over himself and hit his head on a side table, which killed him. Hours later, Bobby came out of his room and found his father unconscious on the floor.
