Viktor Külföldi, real name Jakab Mayer-Rubcsics, born Jacob Mayer (Hungarian: Mayer-Rubcsics Jakab, "Külföldi Viktor") (1844 – March 5, 1894) was a Hungarian Socialist, journalist, and lecturer. Born in Thalheim, Germany (or Switzerland?), he was known in his adopted country by the alias "Külföldi" (Hungarian for "foreigner").In 1871 he became a member of the International Working Men's Association. Together with (1842–1907) and , he co-founded the first Hungarian Socialist organization, the (Hungarian: az Általános Munkásegylet). For organizing a strike by the GWMU, he, among others, was arrested (1871–2) and accused of high treason; he was eventually acquitted because of lack of evidence.