Sirius: A Fantasy of Love and Discord by William Olaf Stapledon

Sirius is Thomas Trelone's great experiment - a huge, handsome dog with the brain and intelligence of a human being. Raised and educated in Trelone's own family alongside Plaxy, his youngest daughter, Sirius is a truly remarkable and gifted creature. His relationship with the Trelones, particularly with Plaxy, is deep and close, and his inquiring mind ranges across the spectrum of human knowledge and experience. But Sirius isn't human and the conflicts and inner turmoil that torture him cannot be resolved.