(Updates with details about Elliott)

By Svea Herbst-Bayliss

NEW YORK, May 25 (Reuters) -

The head of investment stewardship at activist investment firm Elliott Management, Christine O'Brien, has resigned, two sources familiar with the matter said on Thursday, after spending years softening the hedge fund's image as it pushed for changes at big corporations.

O'Brien spent nearly 12 years at Elliott and was named the head of investment stewardship in 2017 to develop better relations between the $56 billion hedge fund and other investment firms, including index funds BlackRock, Vanguard and State Street, broadening the firm's connections in the governance world.

A spokeswoman for Elliott declined to comment and O'Brien could not be reached for comment.

Hedge funds are embracing investment stewardship to develop more collaborative relationships with institutional investors, especially index funds, as these investors place more emphasis on environmental, social and governance factors.

Activist investors like Elliott depend heavily on support from index funds when they wage campaigns for change at corporations that can range from replacing top executives to spinning off units or even selling the entire company.

O'Brien, who earned degrees from Fordham University, joined Elliott's research and finance department in 2011 and was tapped to take on the stewardship role in 2017. She worked closely with Jesse Cohn, one of the firm's managing partners, who has long spearheaded its activist investments.

Elliott's global situational team, which includes the engagement team, has grown in size over the last few years and it is not clear whether O'Brien's position will be filled immediately.

The firm, founded by Paul Singer and now headquartered in West Palm Beach, Florida, earlier this month disclosed a large investment in Goodyear Tire & Rubber Co and wants the company to strengthen its financial position by refreshing the board, selling its stores and conducting an operational review.

In March, Salesforce Inc and Elliott reached an agreement where the activist investor ended its board room challenge as the software company focuses more on boosting profits and efficiency. (Reporting by Svea Herbst-Bayliss; Editing by Muralikumar Anantharaman and Christian Schmollinger)