This monument at Marktplatz is a Baroque equestrian statue depicting Jan Wellem, the Duke of Jülich-Berg. It's one of the landmarks of the city.
Wikipedia (German) http://de.wikipedia.org/wiki/Jan-Wellem-Reiterdenkmal
Address 1 Marktplatz, Düsseldorf 40213, Germany
Coordinates 51°13'33.069" N 6°46'19.112" E