castellón became an american citizen in 1943. during wwii, he was with the oss and assigned to the burma theater. throughout the 1940s and 1950s, his work was informed by his travels abroad: to china with the u.s. army; to italy on his second guggenheim fellowship; and to paris and madrid, where he moved his family for a brief period during which he undertook commissions from american periodicals, including the epic of man series for "life" magazine.