I met him about 10 years ago at a Southern California Botanists event. For someone held in very high esteem by most botanists (the organizers even printed t-shirts with his face on them), he was very humble and down to earth.

Among all of his accomplishments, one of the most important is the paper he co-authored with Paul Ehrlich on the coevolution of plants and the animals that eat them. It demonstrated the "arms race" where plants have evolved the ability to produce toxic chemicals to prevent herbivory while at the same time animals that feed on plants have evolved adaptations that allow them to detoxify these chemicals or otherwise not be affected by them. It is considered one of the foundational papers of modern ecology.

Ehrlich, Paul R. and Peter H. Raven. 1964. Butterflies and plants: a study in coevolution. Evolution 18: 586-608. https://onlinelibrary.wiley.com/doi/10.1111/j.1558-5646.1964...