From his wiki:

Dijon Isaiah McFarlane(born June 5, 1990), known professionally as Mustard(formerly DJ Mustard), is an American record producer. A frequent collaborator of fellow California-based artists YG and Ty Dolla Sign, he began his career producing singles and albums for both rappers, and has since done so for other prominent acts in hip-hop and R&B. He first saw recognition for his work on Tyga’s 2011 single “Rack City”.