Captain Jeffery "Jeff" Manning was the husband of Dr. Natalie Manning and the father of their son Owen. He was KILOD in Afghanistan in February 2015, about 8 months before the start of the series.
Jeff's parents divorced when he was three, and his father remarried and moved to Arizona.
He was married to Natalie Manning until his death and served in the Army Rangers. Natalie was pregnant at the time of his death, but it is unknown whether Jeff knew about the pregnancy.
During "Withdrawal", Natalie loses her wedding ring and panics. She collapses after having a cardiac event and is diagnosed with a condition colloquially referred to as "broken-heart syndrome", brought on by extensive grief. During the same episode, at the suggestion of her mother-in-law Helen, she goes to his grave and leaves the wedding ring to him.
Jeff was killed in action during Operation Enduring Freedom on February 2015. He was 38 at the time of his death, making his birth year 1976 or 1977.