They're named after G Garibaldi (1807 - 1882), the great Italian patriot. Apparently, however, the name for the biscuit was just chosen arbitrarily rather than based on some connection with the man. There is also a garment called a 'garibaldi', which is a woman's blouse. In this case, it really is called after the man himself, because of the type of red shirt worn by his followers.