Quarter Horse, a least in part. He's got a qh body style and those black spots on a red horse are very common on those with some running blood in their backgrounds. Please don't label him mustang because of the head...a lot of mustangs have beautiful faces.
Looks like a Paso fino. Pretty short eaers, gentle expressive eyes, nice compact head, long forelock, short thick neck, nice rump (not too muscular like a QH. Too thick (in the barrel) to be TB. Nice set croup, short coupled, front legs set a little further back than a QH but just like a Paso Fino. Looks like a full blooded Paso to me, I see on other breeds when I look at this horse. Does he gait?