ID the 4 pics and connect. Identifying the guy is difficult, so I'll give an oblique clue - the type of substances he first identified is of immense use in polymer synthesis.

Zuk hits on this - though the answer's quite popular. These are the precursor chemicals on which the Google Gulp Flavors were named. From top, beta carotene (Beta Carroty), Moses Gomberg (discoverer of free radicals, Sugar-Free Radical), Serotonin (Sero-Tonic Water) and Glutamic acid (Glutamate Grape).