Opendoor’s IPO last month crowned CEO Eric Wu a billionaire. It quintupled the value of SoftBank’s stake to $2.3 billion. And it reaped early investor Khosla Ventures a 36x return — on paper. After merging with a blank-check company last month, the iBuyer’s stock closed at $31.25 per share on its next day of trading, Dec. 21, giving it a market capitalization of close to $19 billion. (The stock closed at $28.13 per share on Jan. 7.) Opendoor’s largest shareholder is SoftBank, with a 13.5 percent stake, followed by Khosla Ventures (8.5 percent) and Len Blavatnik’s Access Industries (6.4 percent). A deep dive into regulatory filings confirms the first rule of investing: Betting early yields the biggest returns.