Nothing like the industry now, but the Z-80 and contemporary chips (8085, 6502, 680x) came from companies (Intel, MOS, Motorola) that were as massive as the industry was at the time. The 6502 (Apple, Atari) came out of engineers who left Motorola.

The original ARM chip came from engineers at Acorn seeing first hand how few people were involved in the creation of the 6502 they were using in the BBC Micro and deciding they could have a go at a RISC chip themselves.

There's a lot to be said for having a go to see how far you can get.