Level 90 (Legacy)

Why are you even here?

This is the most straightforward achievement :P

Just to add this for historical purposes, there's always a lot of controversy surrounding World firsts. This was no exception, as the first reported person to attain level 90 achieved this by repeatedly killing Osul Mist-Shaman. Killing them would buff you with Surrounding Mist. FS of Ravencrest EU took advantage of the buff for at least 4 levels. Whether this is cheating or exploiting is for others to debate, as Blizzard decided to roll him back to Level 87. Draw your own conclusions.
For more info, check these links:
http://wow.joystiq.com/2012/09/24/fs-of-ravencrest-eu-gets-world-first-level-90/
http://www.youtube.com/watch?v=GofjSQ5ei1g
Edit: It seems the decision has been reversed!
http://www.mmo-champion.com/content/3216-Brawler-s-Guild-Shirts-World-First-Level-90-April-18-Hotfixes-Blue-Posts-Fan-Art?page=3#comments

I have submitted 2 screenshots the first one I assumed was blurry.

You should see it within 72 hours apparently, oh well!