• Hedge fund manager Bill Ackman was an early investor in e-commerce start-up Coupang, often called the Amazon of South Korea.
• Ackman said he's donated his entire stake in Coupang, worth more than $1 billion, to charity.
• Often called the Amazon of South Korea, Coupang shares Monday were up about 45% from last week's IPO.

Billionaire investor Bill Ackman said Monday he donated his entire stake in Coupang — worth more than $1 billion — to charity following the South Korean e-commerce company's IPO last week.

Ackman, who runs the Pershing Square Capital Management hedge fund, invested his personal money as an early backer of Coupang, CNBC first reported last Thursday on the firm's NYSE debut.

Coupang, often called the Amazon of South Korea, saw its shares nearly double during its first trading day, before closing more than 40% higher. The stock was up around 5% to $51 on Monday, valuing Ackman's gifted 26.5 million shares at more than $1.3 billion.

In a tweet Monday, Ackman said he was a "day one investor" in Coupang, which was founded in 2010 by CEO Bom Kim. Ackman said the Seoul-based company's "incredible success" will now "benefit humanity."

I was a very fortunate day one investor in .@Coupang. 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 non-profit. Thank you to Bom and the Coupang team on behalf of all of us!

— Bill Ackman (@BillAckman) March 15, 2021

Ackman said the money — the breakdown of which was not disclosed — will go to three charitable organizations including his own Pershing Square Foundation.

According to its website, the PSF has committed over $400 million in "grants and social investments across a number of fields, including health and medicine, education, economic development and social justice."

Ackman did not identify by name the two other entities receiving his Coupang shares, calling them only a "DAF," or donor-advised fund, and "another non-profit."

"Thank you to Bom and the Coupang team on behalf of all of us!" Ackman also wrote.

Coupang raised $4.6 billion in its initial public offering last week, the largest so far this year in the U.S. The company ranked No. 2 on CNBC's Disruptor 50 list last year.