There is just one founder of Rivian and that is RJ Scaringe, an MIT graduate. "The company was founded on 4 April 2009 by CEO Robert "RJ" Scaringe, who graduated from the Massachusetts Institute of Technology with a doctorate in mechanical engineering. After being renamed Avera Automotive and then Rivian Automotive, the company began focusing on autonomous electric vehicles in 2011. Rivian received a large investment and grew significantly in 2015, opening research facilities in Michigan and the Bay Area. Relocating headquarters to Livonia, Michigan to be closer to key suppliers, Rivian began working exclusively on electric autonomous vehicles, specifically building an "entire ecosystem" of related products. It also began gearing its prototypes towards the "ride-sharing and driverless car markets." Source: Wikipedia
He did attend RPI (Rensselaer Polytechnic Institute) as well as MIT. Here's a note about him in an alumni publication.