Brendan Foody started Mercor when he was 19 years old. Now he’s 23, worth billions on paper, and running one of the fastest-growing companies in AI history. On Thursday, his $10 billion business acquired startup Deeptune, a company Foody quietly helped fund months before buying it, Fortune learned exclusively. Deeptune, an Andreessen Horowitz-backed startup, builds simulation environments where AI agents practice real-world tasks before touching production systems—think a flight simulator, but f...