Agent Vail was introduced in the episode "Identity" as the team's rookie agent. He was originally partnered with Kensi Blye.
Dom was not a native of Los Angeles. An MIT alumnus, Dom moved to straight to LA after he was recruited by NCIS following graduation.
Dom's field of study was not disclosed, although on several occasions he demonstrated advanced skills with computers and electronics, and a tech guy named Ty stated that he "makes a pretty good geek for a field agent."
As of season 1, both of Dom's parents were still alive. Dom was an uncle, as evidenced by crayon drawings stuck to his refrigerator door.
Dom disappeared in the episode "Past Lives" (although his team did not realize this until the following episode "Missing") and was finally found in the episode "Found". It was revealed that he had been captured by professional kidnappers hired by Islamic militants and held hostage in the hope of facilitating a prisoner exchange.
Although agents Callen, Kensi and Sam eventually found him, they later found themselves caught up in a major gunfight with the terrorists.
While pinned down on the rooftop, Dom spotted another terrorist and screaming Sam's name, rushed into the line of fire, taking the hit, essentially sacrificing himself to save Sam's life before falling to the ground, bleeding and suffering fatal injuries.
Sam dragged Dom to safety before he finished off the first terrorist while Kensi shot the second terrorist and Callen posing as one of Kalil Abramson men's shot Abramson before he and Sam rushed to Dom's aid.
Despite Sam and Callen's efforts to stop the bleeding, Dom died almost immediately with his death leaving the OSP team completely shell-shocked and grief-stricken.
In the aftermath of the tragedy, Sam and Kensi were seen crying while in the office, the majority of the OSP team watched in disbelief as the events unfolded before them. Hetty left the Ops Centre, distraught and later attempted to resign from being the Operations Manager in the next episode, Episode:Hunted but thanks to Callen recovering her resignation letter from Vance, she stayed on.
Dom's role in the team and his position as Kensi's partner was later taken over by LAPD Detective Marty Deeks.
Callen's INTERPOL report at the end of Missing listed Lauren Vail as Dom's mother and Martin Vail as his father who is a retired Army soldier.
- The season 1 episode "Past Lives" was the last to credit Adam Jamal Craig as a main cast member. He was later credited as a guest star in the season 1 episode "Found" which was also his final appearance on the show.
- Dominic's surname, "Vail" can sometimes be misspelled as "Vaile" just like Eric Beale's.
- Like Timothy McGee from the original NCIS series, Dom graduated from MIT and he's skilled in computers.
- Also like former NCIS Special Agent Caitlin Todd, Dom died in the line of duty but unlike Kate who was on the team for a year and a half before her death, Dom's lasted for only a few months before his capture, eventual disappearance and death.
- He is known to speak Spanish and French.
- He is also from or born in Alexandria, Virginia.
- He is 5'11" and weighs approximately 170 lbs.