Two and a half years after becoming CEO of TD Ameritrade, Tim Hockey has resigned, reflecting differences with the giant discount brokerage's board of directors over it future direction.

Neither Hockey nor TD Ameritrade elaborated on those differences. TD Ameritrade has custody of about $1.3 trillion in assets, about half of which are managed by nearly 7,000 RIAs who use its platform.

Hockey came to the brokerage-custodian from TD Bank, where he had worked since 1983. Based in Toronto, TD Bank owns about 40 percent of the discount brokerage's outstanding shares. Hockey was handpicked for the position by former TD Ameritrade CEOs Fred Tomczyk and Joe Moglia, who remains chairman.

Hockey's tenure at TD Ameritrade coincided with its $4 billion acquisition of Scottrade in late 2016. While that transaction helped expand its retail business, it is the RIA custodian business that has attracted the majority of new assets in the past year.

As part of the Scottrade merger transition, Hockey chose to replace long-time TD Ameritrade executive Tom Bradley with Scottrade's Peter DeSilva. At the time, Bradley was running TD Ameritrade's retail business, but he had spent most of his 30-year career at the company and its predecessor firms building the RIA custodial platform.

The move stunned many in the RIA community. Bradley was seen as a consistent advocate for RIAs and he had overcome TD's early reputation as the home for small RIAs by winning the business of giant national RIA firms like Creative Planning and Edelman Financial Engines.

More than most other custodians, he had also managed to maintain clear lines of demarcation between the retail and advisory businesses. During his time running both operations, TD Ameritrade's retail unit targeted primarily self-directed investors and avoided competing with advisors.

Though few advisors were privy to the thinking of TD Ameritrade's board, many of them had assumed the popular and well-respected Bradley was a logical successor to Tomczyk, given his experience running both of its primary business units. They turned out to be wrong.

In a series of conversations with analysts and the media, Hockey said his differences with the board could not be traced to any single factor like M&A. He steadfastly maintained the disagreements were perfectly normal and friendly in nature. However, their conflicts apparently could not be resolved.

In a prepared statement, the board said it would begin a search for Hockey’s successor with the assistance of a nationally recognized executive search firm, adding that internal and external candidates will be considered.

“We are grateful to Tim for his leadership and the contributions he made to the company over his tenure as CEO," board chairman Joe Moglia said in a prepared statement. "He played a key role in the successful integration of Scottrade and has taken important steps to position TD Ameritrade for long-term success. We are pleased that he has agreed to remain in his role to ensure a smooth transition while we conduct our search to identify the right candidate to lead the company in its next chapter of growth.”

Hockey has agreed to stay on in his role until the end of February 2020, according to the release. If his successor is named before that time, he will move into an advisory role to help with the transition.

“The time I’ve spent working alongside my fellow associates at TD Ameritrade has been one of the highlights of my career,” Hockey said in a prepared statement. “Together we embarked on a journey to transform lives and investing for the better, and we’ve accomplished a lot. I believe TD Ameritrade is well positioned to continue as an industry leader and innovator and, until my last day, 100 percent of my energy will be focused on helping our associates drive our strategy forward. I’m intent on keeping our momentum going, and setting up my successor for long-term success.”