They are the result of work by the late Gary Johnson of Guelph.
Wikipedia says this:
In 1953, Johnston was one of the scientists that owned the potato development lab at the Ontario Agriculture College at the University of Guelph.
In 1959 one of Johnston’s graduate students, a young man originally from Peru, told him of a small, rough, deep yellowed flesh potato that was grown by the indigenous communities in his home country.
In Lima this potato variety is considered a delicacy due to its bright color and distinct flavour.
After trying these Peruvian potatoes, Johnston started thinking about creating a variety that would have the same colour and flavor characteristics as these potatoes but would be larger in size and have a smoother shape similar to the potatoes being grown in the “Banana Belt” (Southwestern Ontario).
In 1966 the development team made their first cross between a W5289-4 (2x cross between Yema de huevo and 2x Katahdin) and a Norgleam potato native to North Dakota. After the 66th cross that year, true seed was produced and the G6666 was created.