Elon Musk clinched a deal to buy Twitter Inc (TWTR.N) for $44 billion cash on Monday in a transaction that will shift control of the social media platform populated by millions of users and global leaders to the world's richest person.

It is a seminal moment for the 16-year-old company that emerged as one of the world's most influential public squares and now faces a string of challenges.

Discussions over the deal, which last week appeared uncertain, accelerated over the weekend after Musk wooed Twitter shareholders with financing details of his offer.

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"Free speech is the bedrock of a functioning democracy, and Twitter is the digital town square where matters vital to the future of humanity are debated," Musk said in a statement.

Twitter's shares were up about 6% following the news.