Complex sentence: Arthur Mitchell Ransome (18 January 1884-3 June 1967) was an English author and journalist, best known for writing the "Swallows and Amazons" series of children's books.
Split into simpler sentences: Arthur Mitchell Ransome (18 January 1884-3 June 1967) was an English author and journalist. He is best known for writing the "Swallows and Amazons" series of children's books.