The strongest Viltrumite in the Invincible universe is Thragg, the former Grand Regent of the Viltrumite Empire. He’s not only physically the most powerful Viltrumite, but also the most battle-experienced, ruthless, and strategically brilliant.
Thragg was bred and trained from birth to lead the empire, making him a genetically perfect Viltrumite. His strength far exceeds that of Mark Grayson (Invincible), Omni-Man (Nolan), and even multiple Viltrumites combined. In fact, it took several top-tier characters working together—including Invincible, Battle Beast, and others—just to injure him, and even then, he kept fighting with terrifying endurance.
What makes Thragg especially dangerous is that his raw power is matched by intelligence. He understands warfare, manipulation, and long-term survival, which allowed him to rebuild the Viltrumite threat even after their empire collapsed. His final battles in the series are some of the most brutal and epic in the Invincible universe.