Thomas Sylvester Barthel was a German ethnologist and epigrapher who is best known for cataloguing the undeciphered rongorongo script of Easter Island.

Rongorongo is a system of glyphs discovered in the 19th century on Easter Island. It is not yet known whether rongorongo represents true writing or proto-writing. Numerous attempts at decipherment have been made, but none have been successful so far. Although some calendrical and what might prove to be genealogical information has been identified, none of these glyphs can actually be read. If the system is writing and proves to be an independent invention, it would be one of very few independent inventions of writing in human history.