Santiago Ramón y Cajal is one of the founding fathers of neuroscience. He was the foremost proponent of the neuron theory–that the nervous system is composed of interconnected but individual neurons as opposed to a continuous reticulum of nervous tissue. This conclusion stemmed from his use of the Golgi stain, which randomly stains only a fraction of the cells in a tissue sample, allowing for their individuation. He and Golgi shared a Nobel prize for this work.
Ramón y Cajal was a fantastic artist whose drawings elucidated the structure of the nervous system; the picture above shows two Purkinje cells and a few granule cells from a pigeon cerebellum. There’s now a traveling exhibit of his neuroanatomical work, with an accompanying book. It looks to be a terrific exhibition; here’s a New York Times review, which includes several more wonderful drawings. If you happen to live near one of the tour stops it might be well worth a visit.