Complex sentence: The firm was founded in San Francisco, California in 1914 by Charles Blyth and Dean Witter, known as Blyth, Witter & Co. until 1924--when Witter left to set up his own brokerage business, Dean Witter Reynolds.
Split into simpler sentences: The firm was founded in San Francisco, California in 1914 by Charles Blyth and Dean Witter. Originally known as Blyth, Witter & Co., the firm was renamed Blyth & Co. in 1924, when Witter left to set up his own brokerage business, Dean Witter Reynolds.