This is Isaac Newton's face, frozen in plaster and wax. It's one of two death masks owned by the Royal Society. (The other preserves the face of mathematician, physicist, and early-20th-century science communicator James Hopwood Jeans.) Why take plaster casts of the faces of the dead? The tradition dates back to the pre-photography era where, if you wanted to see what a person actually looked like, a cast (whether of their face in life, or death) was the most accurate way to do it.
The Royal Society has more on the history of death masks, and pictures of the two they own.