Activist hedge fund investor Bill Ackman has donated stock worth $1.34 billion to his Pershing Square Foundation, a donor-advised fund, and a nonprofit.

"I was a very fortunate day one investor in .@Coupang," Ackman wrote in a tweet. "As a result of its incredible success, 26.5m shares of its stock will benefit humanity as I gave all of the shares to @PershingSqFdn, a DAF, and another nonprofit." Coupang is a South Korean e-commerce giant — the founder of which, Beom-su Kim, recently joined the Giving Pledge. Ackman signed the Giving Pledge in 2012.

Last week, CNBC reported that Ackman, founder and CEO of the hedge fund Pershing Square Capital Management, had invested personally in Coupang, which last week raised $4.55 billion in its initial public offering of stock, the largest such offering by an Asian company since Alibaba's IPO in 2014. Forbes estimates Ackman's and Kim's net worth at $3 billion and $8.8 billion, respectively.

Established in 2006, the Pershing Square Foundation has committed more than $400 million in grants and social investments in the areas of health, medical research, education, economic development, and social justice.