The $4.5bn move by Michael Bloomberg's eponymous information and technology company to reacquire Merrill Lynch's 20 per cent stake will not only consolidate his control, but also end one of its most enduring relationships.

Merrill was the first customer when Mr Bloomberg, a former Salomon Brothers executive, founded Innovative Market Systems in 1982. The company, later renamed Bloomberg, specialised in real-time securities data.

Merrill was so impressed with Mr Bloomberg's creation that it paid $30m for a 30 per cent stake in the company. The broker later resold a 10 per cent stake to Mr Bloomberg in 1996 for $200m.

The latest transaction is another indication of Bloomberg's phenomenal growth. The company now claims about 285,000 terminals in operation at a monthly fee of $1,500 each. Revenues were believed to have reached $5.4bn last year.

As Bloomberg has grown, its founder's intentions for it have become an increasing source of speculation in the media industry and on Wall Street - a game that has become more complex with Mr Bloomberg's move into politics.

After becoming mayor in 2002, Mr Bloomberg stepped back from day-to-day operations to avoid conflicts of interest, but has remained involved in strategic decisions, according to his staff. He owns a 68 per cent stake in the operating company.

Two years ago, there was speculation among media bankers that he was preparing to sell - possibly to Microsoft for $16bn - so that he could dedicate more resources to his philanthropic efforts.

Mr Bloomberg's decision to instead tighten his control comes at what may be a critical juncture for the company. The financial institutions that have been its best customers are now cutting jobs amid steep losses.

At the same time, the $17bn merger of Thomson and Reuters - and to a lesser extent, News Corp's acquisition last year of Dow Jones and the Wall Street Journal - have created more muscular competitors.

"For a long time, Bloom-berg had it too easy," Thomas Glocer, chief executive of Thomson Reuters, told the New York Times last month.

Bloomberg, known for its competitive culture, appears to be responding. It recently formed a new venture capital arm and has shifted resources internally to emphasise multimedia delivery on other platforms.