(Adds details, background)
By Michael Flaherty
Oct 6 (Reuters) - A former partner at Pershing Square Capital Management is preparing to launch a new fund, according to a U.S. regulatory filing.
Paul Hilal, who left Pershing Square in January, is launching Mantle Ridge LP, a New York-based investment fund, the filing said.
Hilal was a close lieutenant of Pershing's founder, William Ackman, and was a driving force behind the activist fund's investment in railroad operator Canadian Pacific Railway Ltd . After leading a proxy fight against the company that Pershing Square won, Hilal joined CP's board. He stepped down from that post in January.
Hilal did not immediately return an email seeking comment.
Hilal, who roomed with Ackman at Harvard University, was a Pershing Square consultant in 2006 before joining full-time the following year.
When he left the firm, it was widely expected throughout the activist investor community that he would launch his own activist hedge fund.
The regulatory filing does not detail the precise approach he will take with Mantle Ridge.
Mantle Ridge has a staff of four, according to the July 15 filing.
Hedge Fund Intelligence, an industry news publication and data provider, was the first to report the filing.
Reporting by Michael Flaherty in New York; Editing by Lisa Shumaker and Steve Orlofsky