Michael J. Fox announced he was suffering from Parkinson's disease in 1998, so his role on the show was reduced and costar Heather Locklear was added. But when symptoms of the disease worsened, Fox departed from the show in 2000 to spend time with family and raise money for Parkinson's research. Charlie Sheen stepped into the starring role for the series' last two seasons. In the final season, Fox returned once again to the role of Mike Flaherty.
Best comeback: Fox brought goodwill with him and though it was heartbreaking to see the boyish actor beginning to show the wear and tear of the disease, his return brought pep to a show that was slowly fading away.
--Patrick Kevin Day, Latimes.com