Billionaire Bill Ackman has increased his control of the real estate development company that owns much of downtown Columbia, further tethering the Maryland town’s interests to one of the richest people in the world.

Columbia is among several planned communities owned by Howard Hughes Holdings, a Texas-based developer that Ackman wants transform into a “modern-day Berkshire Hathaway,” the investment conglomerate managed by Warren Buffett. After months of negotiations over a potential merger, Ackman’s private equity firm Pershing Square announced Monday that it reached a $900 million agreement to increase its stake in Howard Hughes from 38% to 46.9%.

The hedge fund will pay $100 per share to snap up nine million newly issued shares in Howard Hughes while giving the company access to Pershing Square’s resources and expertise.

The agreement limits the hedge fund‘s voting power to 40% and its beneficial ownership to 47%, even as it installs Ackman as executive chairman of Howard Hughes’ board of directors.

It‘s not yet clear what the agreement means for Columbia, which is home to about 100,000 people and anchors one of Maryland‘s most affluent counties. The planned suburban community situated between Baltimore and Washington, D.C., was founded in 1967 by developer James Rouse as a model of racial and socioeconomic integration.

What is certain is Ackman’s growing influence over a real estate company that is a key player in downtown Columbia‘s 30-year master plan, which includes major redevelopment projects such as a new library.

Pershing Square previously said a merger with Howard Hughes would not change business for master planned communities like Columbia.

The announcement this week states that Howard Hughes will continue to develop its planned communities like Columbia, “furthering its commitment to becoming the premier residential and commercial real estate developer.”