Elon Musk’s bid for Twitter Inc., which is in question after the billionaire’s threat to walk away, attracted a bevy of big-name backers and Silicon Valley mainstays. But there were some notable exceptions.

High on that list is a Dubai-based investment firm whose assets have surged to more than $5 billion under its secretive founder Alexander Tamas, according to regulatory filings and people familiar with the matter.

Vy Capital — whose main website consists of one page, with no address and no contact details — has committed $700 million to finance Musk’s bid for the social network, making it the third-biggest outside equity investor in a deal that’s drawn money from billionaire Larry Ellison and Sequoia Capital, securities filings show.