Complex sentence: Ogilvy & Mather was founded in 1948 by David Ogilvy, as "Hewitt, Ogilvy, Benson, & Mather" in Manhattan with a staff of two and no clients.
Split into simpler sentences: Ogilvy & Mather was founded in 1948 by David Ogilvy. Ogilvy opened hus US shop as "Hewitt, Ogilvy, Benson, & Mather" in Manhattan with a staff of two and no clients.