Mercedes Diemand-Hartz is a Spanish voice actor known for her extensive work in dubbing anime series and films into Spanish, primarily during the 1990s and early 2000s. Her career is based in Barcelona, a major center for dubbing in Spain. She is recognized for lending her voice to a wide array of female characters, ranging from strong-willed heroines to villainous roles, across many popular and cult-classic anime titles.

Information about the start of her career is limited, but her work is documented from at least the early 1990s. A significant early credit is her role as the voice of Kei in the Spanish dub of the landmark film Akira, which was recorded in Barcelona in 1992. This film also credits her as the dubbing director, indicating her involvement in the industry extended beyond performance. Her voice can also be heard as Brisa in the 2013 Spanish animated television series Pedro y Lola.

Diemand-Hartz's filmography is particularly notable for the number of leading and supporting roles she played in anime OVAs (Original Video Animations) and movies that were distributed in Spain by companies like Manga Films. She voiced the iconic fighter Chun-Li in the Spanish version of Street Fighter II: The Animated Movie. She was also the Spanish voice of Leona Ozaki in Dominion Tank Police, Sayaka Rama in Demon City Shinjuku, Maggie in Venus Wars, and Sarah Cyanbaker in Odin: Starlight Mutiny.

She had several recurring roles across different series. She voiced Biko "B-ko" Daitokuji in the Project A-ko movie and its subsequent OVA sequels. She was also the Spanish voice for multiple installments of the Urusei Yatsura films, playing the role of Lum. In the Tenchi Muyo! franchise, she voiced the space pirate Ryoko. Other prominent roles include Linna Yamazaki in the first three episodes of Bubblegum Crisis, Noa Izumi in the Patlabor movies, and Jury Arisugawa in Revolutionary Girl Utena.

Her work encompasses a wide range of other titles. She voiced Yurina Kirishima in Akiko, Karura in Lunatic Night, Azusa Shiga in The Laughing Target, Mitsuki Sanada in Dual! Parallel Trouble Adventure, Lin-Lin in Night Warriors: Darkstalkers' Revenge, Michiru Saotome in the Grendizer - Getter Robo G - Great Mazinger Kessen! Daikaijuu special, Hinako Shiratori in Ultimate Teacher, Mica Minazuki in Hyper Doll, Mephisto Dance in Hanappe Bazooka, Matsuri Touba in Sohryuden: Legend of the Dragon Kings, and Towa Kannagi in Mermaid Forest. She also provided the voice for Murasaki in the Lupin III OVA, The Fuma Conspiracy.

In addition to her anime voice work, Mercedes Diemand-Hartz has also performed in live theater. In 2019, she starred in the one-woman play Dora en Kafka in Buenos Aires, Argentina, where she portrayed multiple characters, with the lead role of Dora Diamant, the partner of writer Franz Kafka.