Elon Musk, then the world's richest person, changes his Twitter bio to simply "#Bitcoin" on January 29, 2021 -- the price instantly jumps ~$5,000 in an hour, from around $32,000 to $37,000. The move demonstrated the outsized influence a single high-profile endorsement could have on a still-maturing market. Ten days later on February 8, Tesla would announce a $1.5 billion Bitcoin purchase from its corporate treasury, confirming that Musk's signal was backed by serious institutional conviction.
Wikipedia: History of Bitcoin