The Book of Boba Fett employed a Ukrainian company to de-age Mark Hamill's voice

Variety

The company Respeecher was responsible for re-creating and de-aging the actor’s voice on the recent Star Wars series -- without the actor's participation. Hamill’s voice was completely synthesized using old recordings. Alex Serdiuk, the Ukraine-based company’s co-founder and co-CEO, spoke to Variety about the change days before Russia's invasion of his country. According to Variety, "Serdiuk and his team pulled recordings of Hamill from old ADR sessions, video games and old audiobook recordings from the period. With the cleaner audio fed into the ReSpeecher app, Hamill’s younger voice was then artificially created."