Marvel Comics vs Transformers

Connection:

Both are powerful silver-themed comic book characters who served as herald to a colossal, planet-eating entity (Galactus and Unicron respectively) and were bestowed with powers (Power Cosmic and Angolmois energy respectively) so they can find find more planets for their masters to devour, although their own planets (Zenn-La and Cybertron) are still at risk of being consumed

Both were originally different people (Norrin Rad and Megatron respectively) who were transformed into their heralds by their master upon their first meeting albeit in opposite circumstances (Norrin Rad bargained with Galactus by becoming his herald in exchange for sparing Zenn-La, whereas Megatron was forced to become Unicron's herald after giving him an ultimatum

Both also have suffered some mental trauma as a result (Silver Surfer horrified upon sacrificing a planet with life to Galactus while Galvatron went insane after the near-death experience with Unicron)

Also while Silver Surfer is calm, Galvatron is senile and insane