The Pershing Square CEO said he's admired the ridesharing giant since actor Edward Norton introduced him to the app in its early days.

The hedge fund manager said his fund began buying Uber shares in early January and has amassed 30.3 million shares, worth $2.3 billion.

Uber stock hit its highest level since October after Ackman disclosed his Pershing Square hedge fund accumulated a 1.4% stake in the ride hailer.