The “first Dumbledore” usually means two different things, so here’s both quick answers:

  • The first actor to play Albus Dumbledore in the Harry Potter films was Richard Harris , who portrayed him in Harry Potter and the Philosopher’s Stone (2001) and Harry Potter and the Chamber of Secrets (2002).
  • In the story’s timeline, the first well‑known Dumbledore is Professor Albus Dumbledore himself, long before we meet any of his relatives on screen.

Quick Scoop: Who was the first Dumbledore?

On-screen “first Dumbledore”

  • Richard Harris originated the role of Albus Dumbledore in the first two Harry Potter movies, giving the character his initial calm, grandfatherly screen presence.
  • After Harris passed away in 2002, Michael Gambon took over from the third film onward, but Harris is still remembered as the original Dumbledore for movie fans.

In-universe “first Dumbledore”

  • In the books and wider Wizarding World, the Dumbledore family includes Albus, his brother Aberforth, and sister Ariana, but Albus is the first Dumbledore we meet and the central figure tied to the name.
  • Later films like Fantastic Beasts explore more of the Dumbledore family background, but Albus remains the primary and original Dumbledore most fans think of.

Mini forum-style take

On fan forums, when someone asks “who was the first Dumbledore,” most replies split: half say Richard Harris (first movie Dumbledore), and the rest mean Albus Dumbledore as the first famous wizard with that surname in the story.

TL;DR:
If you mean the movies: first Dumbledore = Richard Harris.
If you mean the Wizarding World story: first major Dumbledore = Professor Albus Dumbledore. Information gathered from public forums or data available on the internet and portrayed here.