Gabriel Agreste (born as Gabi Grassette), was a famous fashion designer, and Adrien's strict, overprotective, and emotionally abusive father. He served as the main antagonist of the first five seasons, his motives being to obtain Ladybug and Cat Noir's Miraculouses so he can use their combined power to restore his comatose wife Emilie. He used the Butterfly Miraculous to transform into the supervillain "Hawk Moth", his weapon is a cane and his special power is Akumatization, using Akumas, corrupted butterflies drawn to negative emotions, he could transform his victims into supervillains with special powers. In the fourth season, he became "Shadow Moth" by unifying the Butterfly and Peacock Miraculouses, allowing him to use the ability of Amokization as well and later makes Megakumas that can nullify Ladybug's Magical Charms.

In the fifth season, after getting his hands on every other Miraculous in the Miracle Box by giving the Peacock to Félix, he upgraded into a new form called "Monarch".[11] After losing the Rabbit Miraculous to the heroes and being inflicted with a Cataclysm-induced necrosis, Gabriel establishes a partnership with Tomoe Tsurugi to set up the Alliance System, where he remolded the Miraculous jewels into his personal Alliance Rings, smart rings that allow him to channel a Miraculous' power to a villain using the Alliance System. Monarch temporarily seized the Ladybug and the Cat Miraculous, but their Kwamis, Tikki, and Plagg, managed to stall him long enough for Marinette to take them back. When defeated, after learning Ladybug's identity, losing the Butterfly Miraculous, and finally realizing that he ruined his son's life, he redeemed himself, as he briefly seized the Ladybug and Cat Miraculous from her, and succeeded in reviving his wife Emilie and healing Nathalie by sacrificing his own life while recreating the universe. However, before he died, he asked Marinette not to let Adrien know about the supervillain that he was, but instead, remind him of the times he tried to be a good fathe