The parentage of the McIntosh apple is rather obscure: a farmer in Upper Canada named John McIntosh was clearing some brush on his land in 1811 and found some apple seedlings which were presumed to have grown from some discarded apples of a type popular at the time- Alexander, Snow, and/or St. Lawrence Fall- which cross pollenated and grew. In any case, he transplanted the seedlings and eventually discovered that one of them grew really tasty apples. By 1820 he was selling seeds from this tree, but these didn't produce fruit of the same quality. This problem was solved when McIntosh's son Allen learned about grafting in 1835 and by this method the McIntosh apples retained the qualities of those from the original tree. It really took off after that; the McIntosh is now Canada's national apple, and a lot of apple hybrids are descended from it. It remains popular because it's a good all purpose apple, good for both eating and cooking.
Fruits that shall swell in sunny June,
And redden in the August noon,
And drop, when gentle airs come by,
That fan the blue September sky,
While children come, with cries of glee,
And seek them where the fragrant grass
Betrays their bed to those who pass,
At the foot of the apple-tree.
-From The Planting Of The Apple Tree
by William Cullen Bryant