Stephanie Kellner is a German actress and voice actor known for her extensive work in dubbing foreign-language films and television series into German, particularly in the anime genre. Born on August 8, 1975, in Munich, she began her career in front of the camera as a child actor, appearing in television series during her school years. She later trained at the Schauspielschule Ruth von Zerboni in Munich from 1997 to 2000 and also took a workshop in Los Angeles.

In German voice acting, Kellner is most recognized for providing the German voice of the character Nami from the long-running anime series One Piece. She has voiced the role in the main television series since 2003 and in numerous films and specials, including One Piece Film Red, One Piece Stampede, One Piece 3D2Y: Overcoming Ace's Death! Luffy's Pledge to His Friends, One Piece: Episode of Chopper - The Miracle Winter Cherry Blossom, One Piece: Take Aim! The Pirate Baseball King, One Piece: Django's Dance Carnival, One Piece: Nejimaki Shima no Bōken, One Piece: Mega Mecha Soldier of Karakuri Castle, and One Piece Episode of Merry: Mō Hitori no Nakama no Monogatari. She also voiced the character in the 2023 live-action Netflix adaptation of One Piece.

Beyond One Piece, Kellner's extensive voice work in anime includes a wide variety of roles. She voiced Jackie Rhodes in The Bush Baby, Irma in Violet Evergarden, Reiko Ichinose in Forest of Piano, Maike in Pokémon: Jirachi Wish Maker, and Yuki Kei in Space Pirate Captain Herlock The Endless Odyssey. Other notable anime credits include roles in Sailor Moon (as Naru Osaka), Devilman Crybaby, Fate/Apocrypha, Children of the Whales, and Maquia: When the Promised Flower Blooms.

In addition to her work in anime, Kellner has dubbed numerous live-action films and series. She has been the consistent German voice for actress Jessica Alba in films such as Fantastic Four and its sequel, Machete, and Spy Kids: All the Time in the World. Her other dubbing credits include voicing Kate Fleetwood's character in Harry Potter and the Deathly Hallows – Part 1, Diane Kruger in Unknown Identity, and Diane Stanton in Run for Her Life.

Kellner's career also encompasses on-screen acting, most notably as Nadine Voss in the long-running German soap opera Marienhof from 1993 to 1998. She has appeared in numerous other television series and films, including Alarm für Cobra 11, Die Rosenheim-Cops, Sturm der Liebe, and Inga Lindström. She is also an active stage actress, having performed in various theater productions in leading roles.