Mt. Gox by Ciro Santilli 34 Updated Created
The first Bitcoin exchange. Coded as a hack, and they didn't manage to fix the hacks as the site evolved in a major way, which led to massive hacks.
Their creation is clearly visible on the archive history of bitcoin.org: web.archive.org/web/20100701000000*/bitcoin.org which started having massively more archives since Mt. Gox opened.
Video 1.
One Mistake Brought Down This FBI Most Wanted Hacker by Crumb (2023)
Source. Good overview of Mt. Gox.