Critical Role's The Legend of Vox Machina season 4, premiering June 3, 2026 on Prime Video, has added Jon Heder, Andy Serkis, Sara Ramirez , and Mindy Sterling to its cast . Heder reprises his fan-favorite campaign guest character Lionel Gayheart, while Serkis's role remains under wraps, according to ScreenRant's interview with co-creators Sam Riegel and Travis Willingham. The new season picks up a year after the group's separation as they reunite to face the Cult of the Whispered One.

Jon Heder returns as Lionel Gayheart in the Taryon Darrington arc

Jon Heder,best known for his role in Napoleon Dynamite, is reprising his voice role as Lionel Gayheart, a character originally introduced in episode 99 of the Critical Role campaign during the Taryon Darrington arc. As ScreenRant reported,Heder's Lionel is a comedic foil to Grog and quickly became a fan favorite in just three episodes. The new season dives into the Taryon Darrington storyline with Wayne Brady already cast as Taryon, making Lionel's return a natural fit. Riegel shared that Heder "has been a buddy of theirs from the past" and that they were "so fortunate that he wanted to come back."

Andy Serkis joins as an undisclosed role — a perfect fit for the Whispered One?

Andy Serkis, the iconic actor behind Gollum in The Lord of the Rings and Caesar in Planet of the Apes, has been cast in The Legend of Vox Machina season 4, though his character is being kept secret. Both Riegel and Willingham expressed immense excitement, with Willingham stating it is "no secret that they are enormous Lord of the Rings fans" and that Serkis has been on their casting list "from the very beginning." The report notes that Serkis's vocal range makes him ideal for either a heroic or villainous role. Given the arrival of the Whispered One — the season's main antagonist — many fans speculate Serkis might voice the lich-like deity, a theory the interview does not confirm but hints at.

Sara Ramirez and Mindy Sterling broaden the voice cast

Alongside Heder and Serkis, the new season also brings in Sara Ramirez (Grey's Anatomy) and Mindy Sterling (Austin Powers). ScreenRant's exclusive first look at Lionel Gayheart in season 4 shows him in a tense conversation with an unspecified character and standing next to Scanlan. The addition of Ramirez and Sterling suggests more guest roles from the original campaign may appear as the series adapts the final arcs. The full extent of their characters' involvement has not yet been disclosed.

What remains unknown: Serkis's character and Heder's episode count

Two major questions persist from the ScreenRant interview. First, how many episodes will Jon Heder's Lionel appear in? His original campaign run was only three episodes, but the animated adaptation may expand his role, possibly setting up his eventual adventuring with the Darrington Brigade. Second, Andy Serkis's role is completely under wraps. The report highlights that Elijah Wood — another Lord of the Rings alum — is still "sitting out there" according to Willingham, leaving the door open for future cameos. Until the season premieres, fans can only speculate whether Serkis will voice a hero, a villain, or perhaps even the Whispered One himself.