Sitting still does not suit Michael Bloomberg. Eight months since he left political office, the former mayor of New York has returned to run the market data and financial news group that he owns and which bears his name.

Mr Bloomberg will not take the chief executive title but will formally run the company in which he has taken an increasingly hands-on role in recent months, overseeing new ventures such as a move to increase its clout in political coverage. Dan Doctoroff, Bloomberg's chief executive since 2008, will leave at the end of this year. "It is and has always been Mike's company," Mr Doctoroff said in a statement. "It only makes sense for him to retake the helm."

Mr Bloomberg had indicated he would not go back to the company he founded. But to friends and insiders, it was inevitable.

“He was restless,” one said. “He needed to be involved in something more challenging.”

His energy and intolerance for boredom are well-known. While the former mayor enjoys golf and spending time at his holiday home in Bermuda, he shows little interest in retiring. He has been actively involved at his philanthropic foundation and his gun control advocacy group since leaving City Hall in January.

But the pull from the company he founded proved too great to resist. His presence - in an unofficial capacity, at least - has certainly been felt at Bloomberg since he left the mayor’s office at the end of 2013. He was involved in recent changes to Bloomberg Television, which is broadening its focus beyond financial information, and sanctioned high-profile appointments, such as the hiring of John Heileman and Mark Halperin, a pair of well-connected political journalists, to run a new politics site.

Such moves dovetail with Mr Bloomberg’s interests and ambitions, said one friend. “He can’t run for president because he moved too far to the left. But he wants to be a player in the political discourse . . . this gives him a greater voice.”

Justin Smith, poached from Atlantic Media, is leading the company’s media operation, which grabs headlines but remains a small part of its business: Bloomberg terminals, which provide financial data to 321,000 subscribers, generate more than 80 per cent of its revenues.

Mr Doctoroff oversaw an increase in group revenues from $5.4 billion in 2007 to more than $9 billion in 2014, while its share of the financial information market rose from 26 per cent to 32 per cent, according to the private company.

Mr Bloomberg’s challenge will be to find the next phase of growth in a changed market where its customers are increasingly also competitors. Mr Doctoroff began a process of diversification, emerging markets are providing growth and there are hopes for the media operation, where Bloomberg wants to broaden its influence beyond its core financial audience. When the two have dovetailed in the past, however, the company has found itself in the spotlight.

In 2012, China restricted the number of visas issued to Bloomberg reporters after its investigation into the wealth accumulated by senior members of the ruling Communist party. Sales of Bloomberg terminals in China fell and Peter Grauer, Bloomberg chairman, later said it “should have rethought” the coverage.

Last year Goldman Sachs and JPMorgan, two of its biggest customers on Wall Street, voiced concerns that Bloomberg reporters had used data from the company’s terminals to track the users that they wrote about. Bloomberg eventually changed its data compliance and journalism practices after an independent review confirmed that its reporters had used such data in their news gathering.

Mr Doctoroff managed the fallout in both cases. A former deputy mayor under Mr Bloomberg, he ran New York’s bid to host the 2012 Olympics. The bid failed but the master plan was used as a blueprint for rejuvenating sections of the city.

Mr Doctoroff has strong contacts on Wall Street and in politics, but it is unclear what he will do next: Bloomberg said in a statement that it was likely he would focus on the non-profit sector. “I welcome the opportunity to embark on a new chapter and, in time, will decide what’s next,” he said.

Despite signs that the two men trod on each other’s toes, Mr Bloomberg told the New York Times Mr Doctoroff’s departure was not acrimonious: “The press always wants to write about a battle. There was not a battle,” he said.

Mr Bloomberg, who is worth an estimated $33 billion, left the chief executive’s role open, indicating that he could yet hire a successor to Mr Doctoroff. Until he does, he is back in the hot seat.

“Mike is kind of like God at the company,” Mr Doctoroff told the paper. “He created the universe. He issued the Ten Commandments and then he disappeared. And then he came back.”

Copyright The Financial Times Limited 2014