Medieval variant of Mervyn, resulting from the regular Middle English change of -er- to -ar-. Modern use may represent a transferred use of the surname derived from this in the Middle Ages. It is popular in the United States, where it is associated in particular with the American singer Marvin Gaye (1939–84) and the boxer Marvin Hagler (b. 1954).
Galician, Portuguese, Italian, and Jewish (Sephardic): topographic name from castro ‘castle’, ‘fortress’ (Latin castrum ‘fort’, ‘Roman walled city’): in Galicia and also in northern Portugal a habitational name from any of various places named with this word; in Italy either a topographic name or a habitational name.