West Palm Beach, Florida-based Elliott has been a prolific investor in regulated utilities, pushing for change at U.S. power companies including Duke Energy Corp, Evergy Inc and Sempra Energy.
Rosenbaum, who was a senior portfolio manager at Elliott, spearheaded many of those bets. His role included shaping campaigns and helping to manage existing investments and pursue new opportunities in the sector.
Rosenbaum left in recent days, according to the sources, who requested anonymity as the matter is confidential. The reason behind Rosenbaum's exit could not be learned.
Departures among senior managers are rare at Elliott, which is widely feared and respected in corporate circles and likes to keep a low profile.
Elliott declined to comment. Reuters could not reach Rosenbaum for comment.
Rosenbaum joined Elliott in 2016 from York Capital Management, having previously worked at hedge fund D.E. Shaw & Co and private equity giant Blackstone Inc.
Elliott's current portfolio of power and utilities investments will not be affected by Rosenbaum's departure, one of the sources said, as other investment managers at the firm will continue to oversee those companies.
In recent years, Elliott has pushed for greater focus on regulated operations at U.S. utilities, which have steady cash flow and are able to withstand economic downturns. Often, this has involved pushing for, or supporting, moves by management to spin off or sell unregulated platforms.
Earlier this year, Elliott disclosed a sizable stake in Merrillville, Indiana-based utility NiSource Inc.
Founded by Paul Singer, Elliott Management Corp had $55.7 billion of assets under management, as of June 30.
(Reporting by David French in New York; Additional Reporting by Svea Herbst-Bayliss; Editing by Lisa Shumaker)
By David French