Three highly successful 19th century American apples with very similar names ... here is how to distinguish between them.
In essence, Delicious and Red Delicious are the same variety whilst Golden Delicious is an entirely separate variety.
Golden Delicious was discovered growing in West Virginia in the late 19th century, and is believed to be a seedling of Grimes Golden. Along with Red Delicious it became one of the most widely-grown of all apple varieties in the 20th century.
Almost since it was first found, Golden Delicious has frequently been used in breeding programs for new apple varieties, where it often lends its sweet flavor, crisp texture, and superb keeping qualities.
Golden Delicious is not related to Delicious or Red Delicious.
Delicious was discovered in the 1870s growing in a field in Iowa - it is thought to be a seedling of Yellow Bellflower. The farmer who owned the land made several attempts to remove the tree, but it kept coming back, and in the end he let it grow and was surprised to find the resulting apples were of excellent quality.
The "original" Delicious was first known as Hawkeye before being renamed by the Stark Brothers Nursery who purchased the rights to it in the 1890s. It usually has a red / yellow color.
Delicious it is not related to Golden Delicious at all, but is the sport-parent of Red Delicious.
Red Delicious is a red-coloured sport of Delicious. In fact there are a great number of variants of Red Delicious, as growers sort to gain a competitive advantage by selling redder forms of the original Delicious. However in other respects Red Delicious is very similar to Delicious, and like Delicious, Red Delicious trees are tough, disease-resistant and heavy-cropping.
Red Delicious was one of the top commercial varieties throughout most of the 20th century, and even in 2009 still the most widely-grown apple variety in the USA with 27% of the total production*. That makes it more important than the 2nd and 3rd-ranked apple varieties combined (Golden Delicious 13% and Gala 10%).
*Source: United Nations Economic Commission for Europe.