To quote his eulogy
Albus’s own fame had begun to eclipse
that of his father. By the end of his first year, he would never again
be known as the son of a Muggle-hater, but as nothing more or less
than the most brilliant student ever seen at the school. Those of us
who were privileged to be his friends benefited from his example, not
to mention his help and encouragement, with which he was always
generous. He confessed to me in later life that he knew even then that
his greatest pleasure lay in teaching.
He not only won every prize of note that the school offered, he was
soon in regular correspondence with the most notable magical names of
the day, including Nicolas Flamel, the celebrated alchemist, Bathilda
Bagshot, the noted historian, and Adalbert Waffling, the magical
theoretician. Several of his papers found their way into learned
publications such as Transfiguration Today, Challenges in Charming and
The Practical Potioneer. Dumbledore’s future career seemed likely to
be meteoric, and the only question that remained was when he would
become Minister for Magic.
Harry Potter and the Deathly Hallows
and
Other quills will describe the triumphs of the following years.
Dumbledore’s innumerable contributions to the store of wizarding
knowledge, including his discovery of the twelve uses of dragon’s
blood, will benefit generations to come, as will the wisdom he
displayed in the many judgements he made while Chief Warlock of the
Wizengamot. They say, still, that no wizarding duel ever matched that
between Dumbledore and Grindelwald in 1945. Those who witnessed it
have written of the terror and the awe they felt as they watched these
two extraordinary wizards do battle. Dumbledore’s triumph, and its
consequences for the wizarding world, are considered a turning point
in magical history to match the introduction of the International
Statute of Secrecy or the downfall of He Who Must Not Be Named.
Harry Potter and the Deathly Hallows
Even Rita Skeeter had to admit he'd been a prodigy
Now approaching his eighteenth birthday, Dumbledore left Hogwarts in a
blaze of glory – Head Boy, Prefect, Winner of the Barnabus Finkley
Prize for Exceptional Spell-Casting, British Youth Representative to
the Wizengamot, Gold Medal-Winner for Ground-Breaking Contribution to
the International Alchemical Conference in Cairo
Harry Potter and the Deathly Hallows
He discovered entirely new forms of magic
Members of the Order use their Patronuses to communicate with each
other. They are the only wizards who know how to use their spirit
guardians in this way and they have been taught to do so by Dumbledore
(he invented this method of communication).
JKR: Original Website - FAQ
He was, in later life also ...
Order of Merlin
(First Class), Headmaster of Hogwarts School of Witchcraft and
Wizardry, Supreme Mugwump of the International Confederation of
Wizards, and Chief Warlock of the Wizengamot
The Tales of Beedle the Bard
... so it's hardly like he's been slacking off and just kicking back as head-teacher of the local comprehensive school. He's been actively political and ensured that he used his skills to foster a new generation of inclusive wizardry.
You might also want to note that he was
- The founder of both the original and TNG Order of the Phoenix
- The possessor of the Elder Wand
- The possessor (albeit not simultaneously) of all three Deathly Hallows