The adjectives Great, Dread, and Dead are often applied to Cthulhu:
the secret priests would take great Cthulhu from his tomb to revive His subjects and resume his rule of earth
-- Castro, a Cthulhu cultist
(I can't find a canon source for "Dread Cthulhu", but this phrase, with quotes, has over 10,000 hits on Google.)
Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn (In his house at R'lyeh, dead Cthulhu waits dreaming.
-- Frequent chant of Cthulhu cultists
His actual titles listed here are:
- High Priest of the Great Old Ones
- The Great Dreamer
- The Sleeper of R'lyeh