He was the eldest of eight children born to his parents,[1] Irene née Klug and Robert Donald Cook.
Initially, Cook intended on becoming a farmer, and attended North Dakota State University for a degree in animal science and agronomy.
For his PhD, he attended the University of California, Berkeley to research soil-borne pathogens; he graduated with his doctorate in 1964.
[1] His dissertation was about the interactions and life cycle of Fusarium, a genus of fungi that live in the soil and sometimes cause root disease.
One of his early findings was that the disease take-all could be controlled by continuously planting wheat, which eventually caused the soil to suppress the causative fungus.