Complex sentence: John William Polidori (7 September 1795--24 August 1821) was an Italian-English physician and writer, known for his associations with the Romantic movement and credited by some as the creator of the vampire genre of fantasy fiction.
Split into simpler sentences: John William Polidori (7 September 1795--24 August 1821) was an English writer and physician of Italian descent. He is known for his associations with the Romantic movement and credited by some as the creator of the vampire genre of fantasy fiction.