Planar Champion

"Warrior of a hundred worlds. Mercenary captain of the Blood Wars. Sword of celestial vengeance. The planar champion moves between the planes, always driven to battle. She may be driven by a quest for justice or a thirst for blood, but she is feared throughout the known universes for her prowess."

—D&D 3rd Ed. "Manual of Planes"

Imagine a Time Master but for alternate realities and multiverses. You get someone with the ultimate sense of Walking the Earth, But Now I Must Go, and even The Homeward Journey where the person's wanderlust or adventurous nature doesn't just take them across the world but beyond and between worlds. There is an increased impressiveness when a heroes traits are adapted to not just one grand frontier but billions and billions of them.

Examples of Planar Champion include:

• Kevin Keene (Captain N: The Game Master)
• Roland Deschain (The Dark Tower series)
• Tsukasa Kadoya (Kamen Rider Decade)
• Corwin (and possibly Benedict) of Amber (Book of Amber)
• John Furie Zacharias (Clive Barker's Imajica)
• Will Parry (Phillip Pullman's His Dark Materials)
• The main characters in Sliders. The Sci-fi Channel seasons have them directly confront the Multiversal Conqueror Kromags.
• The Digidestined/Digimon Tamers in the Digimon series.
• Marvel's Exiles
• Orion from Beyond Reality
• Sora from Kingdom Hearts, though the cosmology of the World is sort of weird. Each little universe is separated into distinct worlds, and the World is the designation for the Multiverse.
• Pretty much every heroic Michael Moorcock character. Elric of Melnibone is the most famous but almost all his characters roam the Multiverse. He may even be the Trope Codifier.
• Pretty much any PC in the Planescape campaign setting.