Elon Musk has become the first person estimated to reach a net worth of $US500 billion ($A756 billion), according to US magazine Forbes, largely held in shares of electric carmaker Tesla and aerospace firm SpaceX. It comes as OpenAI, the company behind ChatGPT, also reached a valuation of $US500 billion, following a major share deal, a source revealed. Tesla sales also softened, partly because some potential buyers were put off by Musk’s right-leaning political views and his role in Trump’s federal lay-offs and cost-cutting measures. This represents a bump-up from its current valuation of $US300 billion, underscoring OpenAI’s rapid gains in both users and revenue. The company had authorised sales of $US10 billion-plus worth of stock on the secondary market, the source added.