Complex sentence: His father was Maurice Barrymore, an Indian-born British actor who had been born Herbert Blyth, and had adopted Barrymore as a stage name after seeing it on a poster in the Haymarket Theatre in London.
Split into simpler sentences: His father was Maurice Barrymore, an Indian-born British actor. He had been born Herbert Blyth, and had adopted Barrymore as a stage name after seeing it on a poster in the Haymarket Theatre in London.