Frank had a lengthy marriage to a woman he met while serving in Vietnam, and it is implied they had two sons together. Frank described his marriage as happy. Frank volunteered to serve in Vietnam although he was already employed at the FBI (and could have therefore been exempt from service). During his tour, he was injured, and spent some time recuperating at Walter Reed Medical Center.
He had a close call in the premiere episode of Season 3 when he and agent Aderholt tried to confront Elizabeth as she fled from meeting with a CIA informant. Gaad was punched in the nose and Aderholt was subdued shortly after.
Martha was already working at the FBI when Stan was transferred into his position. His old secretary wanted to come with him, but he felt bad "kicking Martha off the desk" and let her stay. He came to regret this decision as it ultimately led to his early retirement.
Gaad died in Season 4 while vacationing to Thailand. He was preparing to leave his hotel room when three Soviets approached him with a proposal. Gaad didn't wait to hear them out, but turned and ran through a glass door, causing his death. This is clearly not the result the Russians were hoping for; the leader of the three men apologies to a dead Gaad twice, and Arkady is later shown feeling terrible when he gets word the mission went awry. Phillip is also troubled when Stan Beeman tells him what happened to Gaad; he'd included Gaad's trip to Thailand in his report to The Center, based on a conversation he had with Stan while playing racquetball.