Gianni Mantesi was an Italian actor and voice actor, renowned for his extensive and distinguished career in theatre, which spanned over six decades, and for his significant contributions to the world of dubbing. Born in Rome in 1924, his birth name was Giovan Battista Marchesini. He graduated in Literature and honed his craft at the Accademia Nazionale d'Arte Drammatica in Rome, where he performed alongside notable actresses like Giulietta Masina and Anna Proclemer. His professional stage debut was with the company of Ruggero Ruggeri. From 1949 onwards, he became a permanent and prominent presence at the Piccolo Teatro in Milan under the direction of Giorgio Strehler, participating in numerous landmark productions, including over six hundred performances of Il campiello. Throughout his illustrious stage career, he worked with virtually all of Italy's major theatre companies and esteemed directors such as Luchino Visconti, Franco Zeffirelli, and Gianfranco De Bosio.

Alongside his theatrical work, Mantesi built a prolific career in dubbing, bringing his distinctive voice to a wide array of characters in films, television series, and animated works. He was also a dubbing director, lending his expertise to the Italian versions of foreign productions. A prominent example of his live-action dubbing work was providing the Italian voice for Jack Klugman in the television series Quincy.

In the realm of animation, Gianni Mantesi's voice became familiar to Italian audiences through numerous roles. He voiced the character Talkin in the anime film Dragon Quest Saga: Emblem of Roto. In the sports anime series Ashita e Free Kick, known in Italy as Forza campioni, he was the voice of Nonno di Roberto, the protagonist's grandfather. He also voiced Mitsugu Kageyama in the OVA series Super Atragon. Among his other notable anime roles were the village elder on Kanon Island in Saint Seiya, Uncle Chuck in the various Sonic the Hedgehog animated series, and the Master in the educational series Siamo fatti così (Once Upon a Time... Life) and its re-dubbing of C'era una volta... l'uomo (Once Upon a Time... Man). His filmography also included voices in animated films such as La spada dei Kamui and Le ali di Honneamise.

Throughout his career, Mantesi collaborated frequently with a circle of fellow actors and dubbing professionals. His wife, actress and voice actress Grazia Migneco, was a constant collaborator, and they often performed together on stage and in the dubbing studio. Other recurring collaborators included actors from Milanese dubbing circles such as Augusto Di Bono, who also directed the dubbing for Dragon Quest Saga: Emblem of Roto and Super Atragon. In addition to his performance work, Mantesi was dedicated to teaching dramatic techniques and acting, sharing his vast experience with new generations. He also directed several theatrical productions from the 1980s onward, forming his own theatre group. Gianni Mantesi passed away on September 11, 2014, leaving behind a rich legacy in Italian theatre, television, and dubbing.