Galactus has faced defeat multiple times in Marvel canon, though most victories require extraordinary power, strategy, or cosmic-scale beings. Here are notable examples of characters or entities that have beaten or decisively defeated him in specific storylines:

• Franklin Richards (adult) with Reed Richards' guidance
  • Franklin, using the Power of the Beyonders and cosmic-level reality-warping potential, has defeated Galactus in canonical stories. Reed Richards has facilitated this by engaging Galactus with strategic bargaining and promises about Herald status, enabling Franklin to exercise his vast power. This is one of the strongest and most widely cited defeats in Marvel’s cosmic sagas.

• Squirrel Girl
  • In a lighthearted but canonically acknowledged moment, Squirrel Girl defeated Galactus in a major storyline, illustrating that unconventional approaches and optimism can triumph even cosmic threats.

• Doctor Strange (with other cosmic forces)
  • Doctor Strange has contended with Galactus and, in combination with other powerful beings or unique circumstances, has helped avert or neutralize Galactus’s threat in certain arcs. The character’s versatility and the mystic arts have proven capable in high-stakes confrontations.

• Thanos (with the Infinity Gauntlet and/or cosmic artifacts)
  • Thanos has defeated Galactus under the right conditions, particularly in stories where the Infinity Gems (Infinity Gauntlet) or other cosmic artifacts empower him to overcome galactic-scale foes. These showdowns are typically part of larger cosmic crossovers.

• King Thor (Thor in the far future)
  • In certain arcs, "King Thor" (Thor when wielding immense power across time) has fought and defeated Galactus, leveraging his godlike might and cosmic endurance. This showcases the scale at which certain Thors can operate against Galactus.

• Ego the Living Planet (with supportive events)
  • In some narratives, Ego has managed to overcome or outmaneuver Galactus through its own planetary-scale power and allied plotlines, though these outcomes can depend on specific story contexts.

• The Scarlet Witch (with reality-warping power)
  • The Scarlet Witch’s reality-warping abilities, in certain story arcs, have enabled decisive defeats or stalemates against Galactus by altering the cosmic balance.

• Other cosmic entities occasionally alter the dynamic
  • Various abstracts or powerful beings (for example, Eternity, Death, Infinity, Oblivion) can match or outpace Galactus in certain tales, depending on the narrative needs, power scaling, and the authors’ intent.

Notes on the landscape:

• Defeats of Galactus are typically context-dependent, relying on the opponent’s power level, the presence of powerful artifacts, or specific narrative stakes. In most long-running Marvel crossovers, Galactus remains one of the most formidable beings, and only a handful of characters can reliably and repeatedly overcome him.

• Some discussions and lists aggregate multiple instances across different continuities and alternate universes, which can lead to varying interpretations. If you’re aiming for a precise ranking or a specific storyline, it helps to specify the universe (Earth-616, alternate timelines, or comics vs. cinematic portrayals).

If you’d like, I can pull up exact issue numbers and story arcs for any of these defeats or tailor the list to a particular comics run or era.