Mayura

Nathalie Sancoeur, later known as Mayura and Catalyst in her akumatized form, is the secondary antagonist of Miraculous: Tales of Ladybug and Cat Noir. She is the assistant of Gabriel Agreste/Hawk Moth, who manages his mansion and takes care of his son Adrien Agreste/Cat Noir. However, she later decides to use the Peacock Miraculous to help Hawk Moth in his quest to steal Ladybug and Cat Noir's Miraculouses.

She is voiced by Nathalie Homs in the original French dub, and by Sabrina Weisz in the English dub.

Pre-Series / Season 1
Though Mayura herself was absent during this time, her civillian identity, Nathalie, was usually seen at the Agreste Mansion alongside her master Gabriel Agreste and Adrien's bodyguard.

Season 2
Mayura makes her debut in the final episode with the same name "Mayura (Heroes' Day - Part 2)". In the previous episode, "Catalyst (Heroes' Day - Part 1)",. Then, in "Mayura", after Ladybug and Cat Noir defeated Scarlet Hawk Moth, she takes the Peacock Miraculous as Catalyst, and transforms herself into Mayura in order to help Hawk Moth.

Season 3
She will appear in Season 3 as the main antagonist, demoting Hawk Moth to be the secondary antagonist.

Personality
As Nathalie, Nathalie appears to be sensible, smart and dutiful. She obeys every command that Gabriel gave her and she helps Gabriel whenever he needs something (just like in Catalyst where Nathalie makes up a plan for Hawk Moth). Nathalie has a great ability to reason with others, due to her tactful nature.At times Nathalie shows her caring and understanding side, such as talking to Gabriel about Adrien's first Christmas without his mother. It has been greatly hinted that she has feelings for Gabriel,  which explains why she is willing to go so far to help him.

Trivia

 * Mayura is the Sanskrit word for peacock, which is one of the sacred birds in Hindu mythology. It is also a contemporary Hindu name used in many parts of India.
 * While the villain is female, mayura is specifically the term for males, while mayuri is the term for females.