These three mad scientist appear in Floyd Gottfredson's
story "Blaggard Catsle" from November 12, 1932 .
In this story, they want to use Mickey Mouse and Horace Horsecollar
as guinea pigs for an experiment...
Then, they didn't appear until May 14, 1972, in the story "Topolino
e il Dominatore del Pensiero", by Guido Martina (Topolino #859). Since
this story, they appeared very rarely (less than 10 stories). Moreover,
they don't always appear all the three at the same time. We often see only
Doublex and Ecks.
The Doctor Frankenollie seems to have been
inspired by them.
Ecks and Doublex look muck like eachother. Ecks has a black hair, a
black fur, black pupils on white eyes, while Doublex has a brown hair,
no fur, and white pupils on black eyes. They both were black gloves, glasses,
and shoes.
Triplex seem to be their head. He doesn't seem to be the same species
of monkey : he doesn't have a round nose, and he has hands instead of feet
(he doesn't were any shoes). He has long black hair, black fur, and he
is (at least to me) much more frightening that his two friends...
Don't mistake Professor Triplex and Doctor XXX
(The Mad Doctor) !