William J. Ryan, the former chairman and CEO of Portland-based TD Banknorth and one of Maine’s most influential bankers, has been appointed chairman of Massachusetts-based Berkshire Hills Bancorp Inc.’s board of directors, the bank said Monday.

The company also said Lawrence A. Bossidy has retired from Berkshire’s board of directors. Bossidy served as Berkshire’s lead independent director since 2012 and previously served as chairman since 2002.

Ryan, who retired as TD Bank NA chairman in 2010, said in a news release that he was excited when Berkshire Hills CEO Michael P. Daly asked him to take over the chairman spot.

“Berkshire’s franchise is uniquely positioned in regional markets that I know well,” the 70-year-old Ryan said. “I’m convinced that we will forge ahead to achieve our objectives to gain market and wallet share, and to deliver high performance financial results.”

Daly said he and Ryan share the same vision for how to strengthen the company’s position as a leading regional bank.

“I look forward to working with him to achieve this vision,” Daly said.

Ryan has been a major player in Maine’s banking industry for decades. He came to Maine in 1989, after serving as a top executive for banks in Massachusetts. He was named chief executive of what was then Peoples Heritage Financial Group in 1990.

At the time, the country was in a deep recession and Peoples Heritage was being dragged down by bad loans. The bank’s stock price was at an all-time low, and it was under threat of being shut down by the Federal Deposit Insurance Corp.

With help from an economic recovery, Ryan resuscitated Peoples Heritage within his first three years at the helm and turned it into a major player in New England’s financial sector.

Ryan and his management team bought nearly 30 banks and insurance companies in New England and New York over the following decade, making the company, renamed Banknorth, the region’s largest homegrown bank.

Now a target for acquisition, Banknorth faced the prospect of losing its Maine headquarters and suffering massive layoffs.

Out of concern for both employees and shareholders, Ryan struck a deal in 2004 with Canada-based TD Bank, which at the time had no presence in the United States. TD Bank would need the back-office, operations centers that Banknorth had set up in Lewiston and Falmouth, so the retention of most workers in Maine was assured.

TD Bank purchased a controlling interest in Banknorth, and the bank was renamed TD Banknorth. Four years later, TD Bank purchased TD Banknorth outright.

At the time of the takeover, Banknorth had about 2,600 employees in Maine. TD Bank now has more than 3,000 employees in the state.

Ryan already serves on the boards of other companies with a strong Maine presence. He has been chairman of benefit and disability insurance company Unum Group since 2011, and he is a director of health benefits company Wellpoint Inc.

Ryan also is the majority owner of the Maine Red Claws, an NBA Development League basketball team affiliated with the Boston Celtics.

He serves as a trustee of the Libra Foundation and is on the board of advisers at the University of New England.