California postman Rudolph Hass brought back some some avocado seedlings to his home in southern California in 1926 and planted them in his garden. One that wouldn’t bear fruit he just left alone to grow. 

Eventually, this tree bore bear fruit that tasted better than the dominant variety of the day, the Fuerte which had a thin, smooth green skin. The Hass avocado skin, on the other hand, was thicker and darker which was more suited for handling and shipping long distances.  Hass patented his avocado in 1935. Today, Hass avocados account for 80% of the market.

See: “Holy Guacamole: How the Hass Avocado Conquered the World” by Brian Handwerk on the Smithsonian magazine website (2017)