With an income of 150,000 guilders per annum he was by far the richest man in the Netherlands, Egmont coming next with an income of 62,000.

William was well educated.

Though he spoke seven languages and was an eloquent orator, he was called "the Silent" because of the rare discretion that never revealed a secret nor spoke an imprudent word.

In religion he was indifferent, being first a Catholic, then a Lutheran, then a Calvinist, and always a man of the world.

His broad tolerance found its best, or only, support in the Erasmian tendencies of Coornheert.