As this hit financial drama opens Season 6, longtime antagonist Bobby "Axe" Axelrod has left the building. The character's off-camera alter-ego, actor Damian Lewis, opted not to renew his contract, citing a desire to spend more time with his family in the U.K. following the death of his wife, Helen McCrory, last April. Filling that nefarious void is new series regular Corey Stoll, who joined "Billions" last season in the recurring role of self-made billionaire Mike Prince. Paul Giamatti, Maggie Siff, David Costabile and Asia Kate Dillon also return.