Nathalie Sancoeur (aka Mayura) is the secondary antagonist of Miraculous Ladybug. She is assistant to a famous fashion designer, Gabriel Agreste, who is also Hawk Moth. When he was nearly caught by Ladybug and friends, she obtains the Peacock miraculous and becomes Mayura and saves him. She has used it since then.
In "Catalyst", which is part of the "Heroes' Day" special, Nathalie is akumatized by Hawk Moth into Catalyst, a power-enhancing supervillain.