Debbie Reynolds, a Hollywood icon since she won hearts with her buoyant performance in “Singin’ in the Rain,” embarked on the role of a lifetime as a founding member of the Thalians, a charitable organization conceived and sustained by entertainers to promote awareness and treatment of mental health issues. She served as the group’s president almost continuously from 1957 to 2011, adding numerous terms as board chair and frequently presiding over its annual fundraising gala. Her tireless efforts have enabled the Thalians to contribute millions to the Mental Health Center at Cedars-Sinai and to UCLA’s Operation Mend, which helps military veterans recover from the physical and psychological wounds of war. Reynolds has appeared in more than 40 feature films, including “The Tender Trap,” “A Catered Affair” and “Mother,” and received a 1964 Oscar nomination for her lead performance in “The Unsinkable Molly Brown.”