Thomas Sylvester Barthel (4 January 1923 – 3 April 1997)[1] was a German ethnologist and epigrapher who is best known for cataloguing the undeciphered rongorongo script of Easter Island.

From 1953 to 1956 he was a Fellow of the Deutsche Forschungsgemeinschaft, in 1957 a lecturer in Hamburg, and from 4 July 1957 to 1 February 1958 he was a guest researcher with the Institute for Easter Island Studies at the University of Chile.

In order to document rongorongo, Barthel visited most of the museums which housed the tablets, of which he made pencil rubbings.

He was the first scholar to correctly identify anything in the texts: He showed that two lines in the Mamari tablet encode calendrical information.

His proposed identification of four major or prime emblem glyphs was later expanded upon by Joyce Marcus, and the Barthel-Marcus quadripartite partitioning of Classic era Maya sites into four regional capitals and an associated hierarchy of four levels of site importance, became an influential concept in Mayanist research.