Theodorus was a "meridarch" (Civil Governor of a province) in the Swat province of the Indo-Greek kingdom in the northern Indian sub-continent, probably sometime between 100 BCE and the end of Greek rule in Gandhara in 55 BCE.
He is only known from a dedication written in kharoshthi on a relic vase inserted in a stupa in the Swat area of Gandhara, dated to the 1st century BCE (line-for-line translation):
"The meridarch Theodorus has enshrined these relics of Lord Shakyamuni, for the welfare of the mass of the people"
This inscription represents one of the first known mention of the Buddha as a deity, using the Indian bhakti word Bhagavat ("Lord", "All-embracing personal deity"), suggesting the emergence of Mahayana doctrines in Buddhism.
It is also one of the examples of direct involvement of the Greeks with the Buddhist religion in India.
Theodorus is considered as contemporary or slightly posterior to another Indo-Greek named Heliodorus, whose c.100 BCE inscriptions have been preserved in the Heliodorus pillar.