Troy D. Zars (1967–2018) was an American biologist. He studied the relationships between genes, neuronal circuits and behavior in the fruit fly Drosophila melanogaster. Zars co-pioneered the use of transgene expression to locally restore gene function in memory-defective fly mutants, an approach that provided breakthrough insights into the localization of memory traces in the fly brain. With ensuing refinements of the methods of transgene expression and the broadening in the range of transgenes to be expressed, this shaped the field of modern behavioral neurogenetics.