This is "A Study of an Elderly Man in a Cap" by Rembrandt. It's a great example of the 17th-century Dutch genre painting, which often depicted personality types. You can see that the artist has captured the subject's character through his expression and posture.
Notice how the signature, signed "Rembrandt", is located halfway up on the right-hand side. Scientific analysis suggests that this painting almost certainly dates from the 17th century, which is consistent with Rembrandt's working period. In fact, the signature is made with the same paint mixture used to render the dark tones in the man's cloak, indicating a high probability that both were created by the same hand.
However, despite its similarities to Rembrandt's style and technique, most experts agree that this painting was not actually created by the master himself. The signature must therefore be a forgery, but it's interesting to consider who might have made it. Perhaps it was someone from Rembrandt's workshop who was familiar with his working practices. Regardless of its origins, "A Study of an Elderly Man in a Cap" is still a remarkable piece that showcases the skill and attention to detail of its creator.
A Study of an Elderly Man in a Cap hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.