Gustav L. Mayr (12 October 1830 – 14 July 1908) was an Austrian entomologist and professor in Budapest and Vienna.
He was a doctor of medicine in 1856, then taught natural sciences and chemistry in secondary schools in Pest, but he lost his post in 1861, because of the Magyarization laws which prohibited teaching in German in Hungarian secondary schools.
The honorary title of imperial advisor (kaiserlicher Rat) was then awarded to him, after having received the golden cross of merit in 1876.
He donated one of his collections of hymenopterans, bringing together 1,350 species represented by around 5,500 specimens, to the Natural History Museum, Vienna, in 1896.
He was responsible for writing the zoological part concerning ants in the travel report of the Austrian Imperial Novara expedition that circumnavigated the world between 1857 and 1859.