Thunderlord McGuy

Origin

Magi (맥가이) is a pirate under the Whitebeard Pirates in the manga One Piece, and his role in the original work is essentially nil. He is an extra with about one panel of screen time — yet that extra carries the grand epithet "Raikyō" (雷卿, Lightning Lord), and that mismatch is where the meme begins. Few characters have this wide a gap between the weight of their title and the weight they are actually given.

How it became a meme

The first spark was incidental rather than about the character himself. In a Korean One Piece community, a post mocking how thin the roster of Marine vice admirals is cited him in passing, and the contrast — a one-panel extra who nonetheless has an epithet — got laughs, making him a brief meme. Mentions picked up again later because there turned out to be more than one thing to look at: the lofty epithet against an unremarkable design, a screen presence that is oddly not quite zero for an extra, and an ability whose nature is never clearly explained. The pile-up of oddities earned him a second look.

It spread mainly through communities including DCInside's One Piece Burning Blood minor gallery, and a Ruliweb post collecting his panels from the original manga also exists.

Variants

When used as a meme, the deliberately misspaced form "Raikyōmaek guy" is arguably the default rather than the correct one. From there it keeps twisting further into coinages like "Raikyōmaek guy" in Latin script, "cerebral-infarction guy" and "arrhythmia guy" — Korean puns built on how the syllables of his name slide toward medical terms. Precisely because the original name is unfamiliar and awkward to pronounce, it can be bent in almost any direction, which keeps the derivatives coming.

How it is used

To describe anything with an impressive name or title and nothing behind it.
Joking about a character loaded with backstory settings who never actually does anything in the work.
Enjoying the wordplay chain for its own sake — inventing a new variant has become the game.