According to WIKI it's his real name-
"The progenitor of the Terre'Blanche name (translatable as either 'white land' or 'white earth' in French) in the region was a French Huguenot refugee named Estienne Terreblanche from Toulon (Provence), who arrived at the Cape in 1704.
The Terreblanche name has generally retained its original spelling though other spellings include Terre'Blanche, Terre Blanche, Terblanche and Terblans."