An Invincible Season 4 Cameo Resurrects A Storied Transformers Rivalry

Spoilers for "Invincible" season 4 episode 7 "Don't Do Anything Rash" follow.

Season 4 of "Invincible" has heated up into a full-blown space opera, as our heroes help the Coalition of Planets fight against the evil Viltrum Empire. The Coalition's leader is Thaedus (Peter Cullen, most famous as the voice of heroic Autobot leader Optimus Prime in "Transformers"). Between his Christian God-like appearance and wise voice, Thaedus appeared to be a typical "big good" character at first, a la Cullen's aforementioned primary role.

Then, "Invincible" season 3 revealed that Thaedus is a Viltrumite himself. Long ago, he grew disgusted with his people's brutality and conquests. So, he assassinated the Viltrumites' Emperor Argall, for which the Viltrumites call him "The Great Betrayer." When the even more brutal Grand Regent Thragg (Lee Pace) took over, Thaedus developed a "Scourge Virus" to wipe out Viltrumites; he committed genocide on his own people, leaving less than 50 Viltrumites alive.

"Invincible" season 4 episode 2 previously depicted the early days of the virus on Viltrum, and showed how Viltrumites still revere Argall. Now, episode 7 opens with a scene showing Thaedus' betrayal and Thragg's ascension. We finally see Argall in the flesh and hear him talk. Who performs his voice? Legendary voice actor Frank Welker. "Transformers" fans (like this one) spotted an Easter egg as soon as they heard Argall talk.

One of Welker's most famous roles is playing Decepticon leader Megatron, Optimus' nemesis, in the original 1984 "Transformers" cartoon. Casting Welker as the enemy of Thaedus, a character played by Peter Cullen, is definitely intentional. "Invincible" co-creator Robert Kirkman is a big "Transformers" fan, and is currently writing the ongoing "Transformers" comic for his company Skybound Entertainment. (A comic that's already brought big changes for Optimus Prime and Megatron.)

If we're comparing cartoon credentials, Peter Cullen as Optimus Prime is to Frank Welker as Megatron just as the late Kevin Conroy's Batman was to Mark Hamill's Joker. Two definitive voices for a hero and villain, paired off time and time again in new stories. Cullen's Optimus and Welker's Megatron sparred in almost every episode of the first two "Transformers" seasons, before reaching a climactic final battle in 1986's "The Transformers: The Movie." Little did the filmmakers know how enduring this robotic rivalry would be in years to come.

Cullen made his grand return as Optimus Prime in the Michael Bay-directed "Transformers" movie in 2007. Welker, though, was recast as Megatron by Hugo Weaving, who took the part with extreme indifference. Weaving stayed around for the two subsequent sequels, while Welker had to settle for voicing Megatron in some movie tie-in video games.

Pairing Cullen's Optimus off against a Megatron without Welker's voice never felt quite right, which the 2010 cartoon "Transformers: Prime" rectified by bringing both actors back. Welker-as-Megatron practically breaks the fourth wall in his debut scene, proclaiming: "Decepticons, I have returned!" From there, Welker also returned for the latter two Bay movies, "Age of Extinction" and "The Last Knight."

For his return, Welker refined his Megatron voice to sinister new heights. In the original cartoon, Megatron was a bumbling villain with a shouty voice. (That's not a mark against Welker; he was doing what the show called for.) In "Transformers: Prime," Megatron speaks like an erudite king, but there's always a growl of menace underpinning his voice even at his most calm. Megatron first amassed followers with his words, but he's still as bloodthirsty as a gladiator turned warlord should be.

During the flashback in "Don't Do Anything Rash," Viltrumite leaders discuss how to deal with a conquered planet in revolt. Thaedus argues that their subjects will stop rebelling if they rule with a lighter hand, but Argall instead orders his soldiers to cull the planet's population by 25%.

That's a very Megatron-esque move, because Argall is a tyrant just like the Decepticon leader; he preaches rule of the strong and believes his race has the right to "bring order" to the galaxy. Megatron's belief in "peace through tyranny" is an ethos Argall would probably agree with.

Thaedus, too, shares a lot of parallels with Optimus Prime — for good and ill. Optimus typically takes up a protector role to Earth and humanity, feeling a responsibility to prevent the Decepticons from ravaging another world like the Transformers' homeworld, Cybertron. Thaedus' dedication to preventing his race's destructive nature from harming other people is very Optimus Prime-like.

But Thaedus is definitely a "means justify the ends" thinker. On top of his later actions, we see in this episode that he killed Argall by striking from the shadows, hardly the act of an honorable warrior. Optimus Prime sometimes has those tendencies, too. In "The Transformers: The Movie," after the Decepticons ravage Autobot City, Optimus swears that: "Megatron must be stopped, no matter the cost." In "The Transformers: Prime" season 2 finale, Optimus sacrifices a chance to restore Cybertron to save Earth instead, a decision even some of his Autobots question.

In the 2015 video game "Transformers: Devastation," Megatron (Welker) asks Optimus (Cullen): "Cybertron is the center of my universe. How is it not the heart of yours?" In this episode of "Invincible," loyal Viltrumites like Thragg pose almost the same question to Thaedus.

"Invincible" is streaming on Prime Video.