Thomas "Tom" Grace was an agent working for APO. He was recruited by Jack Bristow after the supposed death of Michael Vaughn. He eventually sacrificed his life to save many people when Julian Sark placed a bomb under the APO headquarters.
Before Season 5
Tom had a wife named Amanda Grace who was killed.
Grace is sent to defuse a bomb that Sark had placed onto a subway to destroy APO headquarters. Unable to defuse the bomb, he repeatedly sprayed liquid nitrogen on it, which slowed down the mechanism for a short period of time but did not disable it. He was instructed to leave when the timer got to 60 seconds, but ultimately stayed with the bomb beyond the one-minute threshold in order to keep it from going off. His last words were to Rachel Gibson, telling her that he wished they had more time because he would have asked her out. Starting to cry, Rachel responded that she would have said yes. As the time reached the last few seconds, Tom let out a brief laugh glad that he would be reunited with his wife and thankful that Rachel would have said yes. It exploded and killed him instantly (Reprisal).