Doe posted...
is the rule of 2 thing EU? Were Maul, Dooku and Palpatine all active siths at the same time?
It has been a thing since Darth Bane started it in all continuities.
In Legends, Dooku only teamed up with Sidious after Maul was defeated in Episode 1.
In Disney Canon, Tales of the Jedi revealed they teamed up before Maul's defeat in Episode 1.