Mike Lazaridis and Jim Balsillie, the co-chief executives of Research In Motion, have resigned following months of investor pressure for a change at the helm of the struggling BlackBerry maker.

Chief operating officer Thorsten Heins was named president and CEO of the Waterloo, Ontario-based RIM, which has been steadily losing market share to Apple's iPhone and handsets powered by Google's Android software.

Heins, 54, joined RIM from German industrial giant Siemens in December 2007 and served as senior vice president for hardware engineering before becoming chief operating officer for product and sales in August 2011.

"There comes a time in the growth of every successful company when the founders recognize the need to pass the baton to new leadership," Lazaridis said in a statement on Sunday.

He said RIM was "entering a new phase, and we felt it was time for a new leader to take it through that phase and beyond."

Barbara Stymiest, 55, was named chairman of the board, a post previously also held jointly by Balsillie and Lazaridis, who founded RIM in 1984.

Stymiest, who has been on the RIM board since 2007, has held senior positions at the Royal Bank of Canada and was chief executive of TSX Group Inc., operator of the Toronto Stock Exchange.

The management shakeup follows a series of setbacks for RIM including a costly delay in the launch of the BlackBerry 10, the commercial failure of the PlayBook tablet computer and an embarrassing email outage.

RIM shares have lost nearly three-quarters of their value over the past year and the company has been the subject of persistent takeover speculation. Several large investors have been clamoring for a change at the top.

While Lazaridis and Balsillie are handing over day-to-day control they are not stepping away entirely.

Lazaridis, 50, was named vice chairman of its board and chairman of a new innovation committee, offering "strategic counsel" and promoting the BlackBerry brand worldwide.

Balsillie, also 50, will remain a member of the board of directors. "I agree this is the right time to pass the baton to new leadership, and I have complete confidence in Thorsten, the management team and the company," he said.

Lazaridis said Heins, a native of Germany who served as chief technology officer at Siemens, has "demonstrated throughout his tenure at RIM that he has the right mix of leadership, relevant industry experience and skills to take the company forward.

"I am so confident in RIM's future that I intend to purchase an additional $50 million of the company's shares, as permitted, in the open market," he said.

In a statement, Heins said he was confident that RIM was on the right path.

"We have a strong balance sheet with approximately $1.5 billion in cash at the end of the last quarter and negligible debt," he said.

"We reported revenue of $5.2 billion in our last quarter, up 24 percent from the prior quarter, and a 35-percent year-to-year increase in the BlackBerry subscriber base, which is now over 75 million."

According to industry tracker comScore, however, RIM's share of the US smartphone market declined during the three months ending in November, while Apple and Android both made gains.

RIM saw its share of US smartphone subscribers fall to 16.6 percent at the end of November from 19.7 percent at the end of August, according to comScore.

Android was the top smartphone platform with a 46.9 percent share of the US market at the end of November, up from 43.8 percent. Apple's market share also rose during the period -- by 1.4 percentage points to 28.7 percent.

Stymiest, RIM's new chairman, praised outgoing CEOs Lazaridis and Balsillie.

"They created RIM, nurtured it, and in the process not only built an iconic brand, but literally pioneered the smartphone industry," she said. "It is Canada's largest tech company and one of the largest in the world."