Complex sentence: Donald Sigmund Stralem (1903-1976) was an investment banker and philanthropist who worked as a partner in Hallgarten & Company and then served as chairman of Stralem and Company, an international investment bank that he founded in 1967.
Split into simpler sentences: Donald Sigmund Stralem (1903-1976) was an investment banker and philanthropist. Stralem worked as a partner in Hallgarten & Company and then served as chairman of Stralem and Company, an international investment bank that he founded in 1967.