The world’s richest man donated more than 5 million shares in the electric automaker from Nov. 19 to Nov. 29, according to a filing with the Securities and Exchange Commission. The gift was worth about $5.7 billion, based on average prices the days he sold the stock, making it one of the biggest to a charity in history. An unidentified trust was involved in the transaction, and the name of the charity wasn’t cited in the document.

The donation occurred as Musk, Tesla’s chief executive officer, battled with politicians including Bernie Sanders and Elizabeth Warren over inequality and a potential wealth levy. Around the same time, Musk suggested he’d sell stock if the United Nations could prove it would help solve world hunger after the head of the organization’s food-aid arm suggested billionaires like Musk should “step up now, on a one-time basis.”

A large gift to charity last year would help reduce what Musk claimed would be the biggest tax bill in U.S. history. Bloomberg calculated in December that Musk could owe more than $10 billion to the Internal Revenue Service, triggered by his exercise of an unusually large number of options in 2021.

Musk has an eponymous foundation that’s become more active over recent years, with large, eight-figure gifts promised to the city near his South Texas spaceport, a $100 million competition for carbon removal and $5 million to two scientists for COVID-19 research. Before then, his foundation’s largest contributions were to donor-advised funds, or DAFs, where charitable money can sit in perpetuity. 

The Musk Foundation, which used to count Musk’s brother Kimbal as a director, has recently added a new face to its roster. Several grant recipients Bloomberg spoke with have said their primary point of contact at the foundation is Igor Kurganov, a professional poker player-turned-philanthropist who is active in the effective altruism space.