@ossobuco,
Well, hello, Dali!
Seriously, with those images of Dali, it shows the darker moustache is pencil thin..(Van dyke styled) whereas in many paintings of Rembrandt it shows Rembrandt's rather lighter wispy moustache.
Therefore, I'm no longer confident that is Rembrandt. Shrugging shoulders. Unfortunately, I could find nothing online attributing that image to anyone nor naming the subject of the painting.