Petro Evstaf'evic Stojan (Russian: Пётр Евстафьевич Стоян, also known by the pseudonyms Ribaulb, Radovich and Šulerc) (June 22, 1884 in Izmail, Bessarabia — May 3, 1961 in Nice) was a Russian esperantist, bibliographer and lexicographer and a member of the Esperanto Language Committee (Lingva Komitato) from 1914.

In 1929, his Bibliography of the International Language (Bibliografio de Internacia Lingvo) was published.

He also wrote a great number of scientific articles and original literature in Esperanto.

In France he worked on La Vindiania, a thesis on the origin of the Indo-European languages and on a complete philosophy of life, which he named biosophy (in Esperanto - Biozofio).

However, his works remained in the manuscript form and circulated among his friends, and only one book was actually published in 1946 in Arras.