As expected, Los Angeles Department of Water & Power general manager Ron Deaton submitted his resignation Friday, three months after suffering a near-fatal heart ailment.

Deaton, 64, was on medical leave since the onset of the acute heart arrhythmia put him in a coma for two days and prompted an emergency airlift out of Costa Rica, where he was vacationing in July.

A 42-year City Hall veteran, Deaton exerted tremendous behind-the-scenes influence when he served as the City Council’s chief legislative analyst from 1994 to 2004, earning the label, “most powerful person in City Hall.” He’s credited with helping to mobilize City Hall to fight the secession movement in the San Fernando Valley.

In Dec. 2004, then-Mayor James Hahn tapped Deaton to run the DWP, which provides water and power to 3.8 million residents and businesses. During his tenure, the agency came under criticism for seeking rate hikes. The DWP also responded to numerous crises, including a wave of heat-induced blackouts in 2006 largely blamed on antiquated equipment.

Upon receiving word of Deaton’s resignation, Los Angeles Mayor Antonio Villaraigosa said, “On behalf of the entire city, I want to thank Ron Deaton for dedicating a brilliant 42-year career to Los Angeles. This is a man who literally did it all for Angelenos. He kept the lights on through fires and blackouts. He balanced the books. He helped build parks, police stations and libraries. He kept us united as one city.”

While Deaton has been in rehabilitation, the agency’s chief operating officer, Robert Rozanski, has served as acting general manager.

David Nahai, who until last week was president of the DWP Board of Commissioners, resigned that post to put his name forward as a candidate to replace Deaton as general manager.