Here are a few of Elminster's accomplishments:
- Recognized as one of the most famous and powerful wizards in all of Faerun
- Slew an elder orb beholder
- Took part in re-founding the Harpers
- One of Mystra's chosen and also a weave anchor
- Writer of multiple books
- Had a drink named after him "Elminster's Choice"
If you'd like to know more about Elminster Aumar, here is his wiki page.