The name Dietrich is a boy's name of German origin meaning "ruler of the people". Dietrich and is often added to lists like Names That Mean Ruler or Royal and discussed in our forums with posts like "Sibsets you know".
From the experts:
This form of Theodoric, familiar via Marlene, is a possible German import. It is an Anglicized ancestor of Derek and all its variations. A noted bearer was acclaimed classical German baritone and conductor Dietrich Fischer-Dieskau, and there have been Dietrichs in Henry James's The Princess Casamassima,/em and more recently on the TV show Psych.