If you don't count his earlier internet work, he's still active in 3 difficult industries. He's also chairman of SolarCity, a solar panel installer with some innovative financing options. I think he had the idea for the company and provided funding, and his cousins (?) are running it.
He has invested a considerable amount of money in SolarCity and oversees the board; both are indispensable as the former allowed SolarCity to scale (which was the main problem with lowering installation costs outside of material procurement) and the latter has provided the Rives guidance when they needed it.
But as Musk has said, his main role at SolarCity is showing up to the board meeting and hearing the great results.