That would be Rood, who states he is a 'former member of Team Plasma'.
...we're former members of Team Plasma. Because of the incident two years ago, we started taking care of the Pokémon that were separated from their Trainers as a way to atone for our misdeeds.
"Aah! I will say it as many times as it takes until you understand! Ghetsis's real plan was to take over the Unova region! Liberating Pokémon was nothing more than an excuse! If anything, it would've made Pokémon suffer!"