Viriathus (known as Viriato in Portuguese and Spanish) (died 138 BCE) is the most important leader of the Lusitanian people that resist Roman expansion into the regions of Western Hispania (as the Romans will call it), where the Roman province of Lusitania will be established (in the areas comprising most of Portugal, Extremadura and south of the Douro river in Spain).

Viriathus leads the Lusitanians to several victories over the Romans between 147 BCE and 139 BCE before he is betrayed to the Romans and killed.