The investor is closely tracked and has owned this stock for many years.Bill Ackman is one of the most followed investors of the 21st century. The billionaire and manager of the $10 billion-plus hedge fund Pershing Square espouses a Warren Buffett-style investing strategy. He aims to build a concentrated portfolio of high-quality stocks that he can hold for many years. Many of Ackman's stock positions are over 10% of his portfolio. One stock he has owned since 2018 is Hilton Hotels (HLT 0.62%). Shares are u ...