Caption: Portrait identified---wrongly, but traditionally---as that of Thomas Bayes (1701?--1761), discoverer and eponym of Bayes' theorem.

Pierre-Simon Laplace (1749--1827) and Harold Jeffreys (1891--1989) greatly extended Bayesian probablity theory and Bayesian inference.

Harold Jeffreys is one of the "cousins":

Credit/Permission: anonymous artist, 19th century (uploaded to Wikimedia Commons by User:Limojoe, 2011) / Public domain.
Image link: Wikimedia Commons.
Local file: local link: thomas_bayes.html.
File: Art file: thomas_bayes.html.