This is the Remastered Tyrian Graphics pack (original source) created by Daniel Cook, from lostgarden.com.  This pack has 47 tilesets.

License

This  pack is licensed under the Creative Commons Attribution 3.0 License. The author also has a license page that explains its use a little bit further.

Art attributions

If you use this pack, please include the following attribution in a visible location along with any other credits:

"Remastered Tyrian Graphics" art by Daniel Cook (Lostgarden.com)

When possible link to blog post that discusses the original art collection. For this asset pack, it would be “Remastered Tyrian Graphics” art by Daniel Cook (Lostgarden.com)

About the artist

Daniel Cook
I’ve been a game designer, pixel artist, toolmaker, physicist and MBA. My first job in college was on a game called Tyrian at a tiny company called Epic Megagames. These days, I’m the Chief Creative Officer at Spry Fox.