While Theranos' valuation once exceeded a billion dollars, it also absorbed and spent $600M in cash. Where did that come from? Wall Street Journal provides a listing based on court documents.
High profile investors included the Walton family (Walmart; $150M), Rubert Murdoch (Fox; $121M), the DeVos Family (Betsy DeVos, Education Secretary; $100M); the Cox family (media; $100M). Runners-up include Carlos Slim, the Mexican billionaire, and others including the ex-chairman of Bechtel and the owner of the New England Patriots.
My library of a couple hundred media Theranos links, 2014-2016, is here.