Twitter's stock jumped 27% following Elon Musk news

Twitter's stock was up 27% Monday, closing at nearly $50, after the morning news of Elon Musk becoming its largest shareholder.

Why it matters: There had been speculation Musk could buy Twitter. He recently tweeted that it was "failing to adhere to free speech principles" and that he was "giving serious thought" to building a new platform.

The latest: On Tuesday, Twitter announced Musk will join its board of directors.

• "Through conversations with Elon in recent weeks, it became clear to us that he would bring great value to our Board," CEO Parag Agrawal tweeted. "He's both a passionate believer and intense critic of the service which is exactly what we need on @Twitter, and in the boardroom, to make us stronger in the long-term."
• Musk replied, "Looking forward to working with Parag & Twitter board to make significant improvements to Twitter in coming months!"
• Being on the board means Musk won't be able to buy more than 14.9% of the company's stock.

State of play: Musk's 9.2% ownership stake, made on March 14 and revealed in an SEC filing Monday, was worth $3.68 billion at yesterday's market close.

• Musk has been a prolific Twitter user and has more than 80 million followers. He shares memes, replies to Tesla fans and critics and sometimes gets in trouble with the SEC.

• Musk had not shared much about his investment until Tuesday. He tweeted Monday, "Oh hi lol." He later tweeted a poll asking if users wanted an edit button.

What we're saying: Axios Pro Rata writer Dan Primack noted the "last time an activist investor faced off with Twitter, it ultimately resulted in Jack Dorsey's departure."

• Axios Closer writer Hope King wrote, "Musk has often posited that we're all living within a simulation. Well if he has his way, we will be — WITHIN HIS."