The avocado as you know it was a total accident:
All commercial, fruit-bearing Hass avocado trees have been grown from grafted seedlings propagated from a single tree which was grown from a seed bought by Rudolph Hass in 1926 from A. R. Rideout of Whittier, California. At the time, Rideout was getting seeds from any source he could find, even restaurant food scraps. The cultivar this seed came from is not known and may already have been cross-pollinated when Hass bought it.
In 1926, at his 1.5-acre grove at 430 West Road, La Habra Heights, California, Hass planted three seeds he had bought from Rideout, which yielded one strong seedling. After trying and failing at least twice to graft the seedling with branches from Fuerte avocado trees (the leading commercial cultivar at the time), Hass thought of cutting it down but a professional grafter named Caulkins told him the young tree was sound and strong, so he let it be. When the tree began bearing odd, bumpy fruit, his children liked the taste. As the tree's yields grew bigger, Hass easily sold what his family didn't eat to co-workers at the post office.