Sir Christopher WREN was an English architect, scientist, and mathematician who is best known for designing St. Paul's Cathedral in London. He was a key figure in the rebuilding of London after the Great Fire of 1666 and designed many other churches, monuments, and public buildings. He was knighted in 1673 and was later appointed Surveyor-General of the King's Works. His surname, WREN, is derived from the Old English word for 'WREN, ' a small bird.