Jack is James' younger half-brother. Like the rest of his brothers, Jack never knew who his father was, but now is the only one who doesn't know, though he expects its James' father, Sam.
On the dating scene he and Barney are a lethal combination as James is as effective a homosexual charmer as his brother is with the opposite sex.
James eventually married Tom, contrary to Barney's initial protests. Barney was not specifically opposed to gay marriage, but to the general concept of monogamy for any two people of different orientationsa. When Barney learned he was going to be an uncle, he came around. In fact he was best man at the wedding.
Like Barney, James enjoys Laser Tag, fine suits, and maintaining a blog. Also, like Barney, James also grew up not knowing who is father was, although his mother suggested several black celebrities: Bill Cosby, Flip Wilson, James Earl Jones, and Meadowlark Lemon. It wasn't until 2010 when Loretta moved out of James, Jack and Barney's childhood home did he discover a clue that lead him to his birth father: Sam Gibbs.