Spoilers for "Invincible" season 3 to follow.

Robert Kirkman first worked with Steven Yeun when the latter played Glenn on "The Walking Dead" (a series based on Kirkman's long-running zombie comic). Then, when Prime Video turned Kirkman's superhero comic book "Invincible" into an animated show, Yeun got the series' leading role.

The cast of "Invincible" has since included a handful of other "Walking Dead" alums. The latest of them came the end of season 3 when Jeffrey Dean Morgan, who played the baseball bat-wielding apocalypse warlord Negan, arrived as the Viltrumite warrior Conquest. ("The Boys" isn't the only superhero show out there with Mr. Morgan in its cast.)

Conquest is one of the oldest, most powerful, and most monstrous Viltrumites. In the season 3 finale, "I Thought You'd Never Shut Up," Conquest gives Invincible the fight of his life. But there's one Viltrumite out there who leaves even Conquest trembling in his...