Marvel Comics has a near endless cast of resourceful, dedicated, and relentless heroes, but when they faced their ultimate threat, Doctor Strange identified the one he believes in more than any other. Faced with an omnipotent villain, the Sorcerer Supreme nevertheless bet on one superpowered ally to come out ahead.
Secret Wars was a massive event where Doctor Doom stole the power of the Beyonders', saving the multiverse by crafting its remains into a single "Battleworld" under his godlike control. Doctor Strange - who helped Doom in his quest to save something from the Beyonders' deadly incursions - made the best of this new reality, operating as a sheriff to the various domains to enforce Doom's will and study what remained. Thankfully, Doom wasn't left to his own devices indefinitely, as two craft survived the destruction of Marvel's mainstream Earth-616. One carried a group of villains led by Thanos, while the other carried Earth's last heroes, including Black Panther, Reed Richards, and X-Men's Cyclops.
When Doctor Doom confronted the heroes and villains, Doctor Strange magically scattered them across Battleworld, knowing Doom would kill them. It was a major betrayal of their partnership, and one Strange knew Doom would execute him for. With nothing left to lose, Strange called out Doom for stealing Reed Richards' family in his new world, and accused the 'God Emperor' of being afraid of Mister Fantastic. "Even with all this power, you're still afraid of him," Strange asserts. "I think you should be." As intended, he hits a nerve, and Doom kills him then and there.
Faced with the greatest heroes and villains of the Marvel Universe, Doctor Strange identified Reed Richards as the true threat to a seemingly unbeatable opponent. Doom had ruled Battleworld for years, while to Mister Fantastic it was a strange and totally unfamiliar place. Nevertheless, Strange identified that even a seeming god should fear Reed Richards - and he was right.
Even though his sheer might allowed God Emperor Doom to easily overwhelm all the powerful forces fans believed were the strongest in the universe, he ended up being no match for Reed Richards’ sheer determination and ability to strategize. Often, Mister Fantastic is obsessed to unhealthy levels, harming his familial and working relationships, as well as himself. Yet it is this same dogged determination and ingenuity that allows him to reach a level of heroic greatness that permits him to punch far above his weight class. He succeeded where a Cyclops imbued with the Phoenix Force, the mad Titan Thanos, and an Infinity Gauntlet-wielding Black Panther failed, baiting Doom into a situation where he can be defeated.
Reed then oversaw the creation of a new universe in which his former allies were recreated, though not truly resurrected, meaning that Doctor Strange's words of belief in him were the final words of the hero fans had been following for decades. Doctor Strange correctly foreshadowed who would end Doctor Doom’s seemingly insurmountable reign, picking out Reed Richards as the one Marvel hero who can truly rise to any challenge, even in situations where the Sorcerer Supreme himself has been bested.