Ralph Whitworth, co-founder of San Diego-based Relational Investors, an activist money management firm, has taken a leave of absence from the firm and resigned as interim chairman of Hewlett-Packard Co. to focus on his health, Relational said.

Whitworth duties at the $6 billion-asset money firm are being assumed by co-founder David Batchelder and other members of the management team.

According to Bloomberg, which quoted people familiar with the issue, Whitworth, 58, is battling cancer.

Whitworth and Batchelder founded the firm in 1996, obtaining a $200 million investment from the California Public Employees’ Retirement System, the nation’s largest pension fund.

The firm invests in a variety of public companies, taking stakes large enough to provide some influence on how a company is operated. Over the years, the firm has helped turn around such companies as Home Depot Inc., Genzyme Corp. and Sprint Corp., according to Bloomberg.

In 2011, Whitworth joined Meg Whitman, the CEO of Hewlett Packard, in a massive restructuring that resulted in the elimination of 34,000 jobs at the PC manufacturer.

Whitworth is also known for hiring Paul McCartney to play a concert at his home celebrating his wife’s 50th birthday.