Thomas Henry Huxley PC PRS ( 4 May 1825 â `` 29 June 1895 ) was an English biologist . He was known as Darwin 's Bulldog for his support of Charles Darwin 's theory of evolution . Thomas Henry Huxley PC FRS ( 4 May 1825 â `` 29 June 1895 ) was an English biologist , known as `` Darwin 's Bulldog '' for his advocacy of Charles Darwin 's theory of evolution .