The Granny Smith apple is named after Maria Smith, an orchardist in Ryde, Sydney. Maria discovered the apple growing on her property as a ‘sport’ from some French crab apples. As a true mutation, the original seedling gave rise to more, which were originally exhibited as “Smith’s seedlings”, then “Granny Smith’s seedlings”, and finally just “Granny Smith’s”. The apples remained a local curiosity until after Maria Smith’s death, the first large-scale cultivation not taking place until 1895.
Apples are largely propagated by cloning. Many varieties have been lost over the years. An interesting article about the origin of apples was published in The Atlantic in February 2013.