6. Morris O'Brian
Introduced in season five as essentially a comic relief character, Morris O'Brian was the unlikely British ex-husband of Chloe. Charming and likable, he quickly grew on fans, and so became a recurring character in seasons six and seven, where he got back together with Chloe, and then they eventually had a son, Prescott. Morris was curiously missing for season eight - though does appear on the Blu-ray epilogue when Chloe is arrested for helping Jack - though given that Chloe is returning for Live Another Day, why not throw Morris in the mix too? Granted, someone has to watch their son, but his supreme tech skills would make him great support for whatever operation Jack is running. Plus, the rather uneasy nature of his and Chloe's romantic relationship could make for some welcome comic relief.