Albert Einstein was a theoretical physicist, widely acknowledged to be one of the greatest physicists of all time. Einstein is known for developing the theory of relativity, but he also made important contributions to the development of the theory of quantum mechanics.

Einstein did talk about "the god of Spinoza" but seemed to see these in a firmly naturalistic context. He preferred to describe himself as agnostic rather than atheist. He did not believe in a personal god or an afterlife saying "No. And one life is enough for me." He served on the advisory board of the First Humanist Society of New York and was an honorary associate of the Rationalist Association. He also said: "The word God is for me nothing more than the expression and product of human weaknesses, the Bible a collection of honorable, but still primitive legends which are nevertheless pretty childish. No interpretation no matter how subtle can (for me) change this. ... For me the Jewish religion like all other religions is an incarnation of the most childish superstitions. And the Jewish people to whom I gladly belong and with whose mentality I have a deep affinity have no different quality for me than all other people. ... I cannot see anything 'chosen' about them."

He seems to have been vegetarian by the end of his life. He said: "Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures..." and “If a man aspires towards a righteous life, his first act of abstinence is from injury to animals.”

Thanks to @its_sethlee for suggesting Einstein as a "proto-Sentientist" and for his research shared in our Sentientism FaceBook Group (all welcome - Sentientist or not!).

Einstein on Wikipedia