expositor (n.)

• annotator
• author
• cicerone
• commentator
• critic
• cryptanalyst
• cryptographer
• cryptologist
• decoder
• demonstrator
• dragoman
• editor
• editorialist
• essayist
• exegete
• exponent
• expounder
• glossarist
• go-between
• guide
• interpreter
• lecturer
• lexicographer
• preacher
• publicist
• reader
• reviewer
• scholiast
• sermonizer
• translator
• writer