Bionicle is a line of buildable figures created in 2001 by lego. Bionicle's story follows several different teams of biomechanical elemental warriors known as the Toa on their quest to defeat the evil master of shadows, Makuta. The line was one of the most successful lego themes of all time and it ran until 2010, when it was discontinued. Bionicle was brought back once again in 2015, however despite some very good sets it did not sell very well and was cancelled prematurely only one year later in 2016. Despite this, there still exists a large dedicated fanbase, who keep the spirit of the Bionicle alive thanks to their amazing creativity.

Bionicle's story is told in multiple different types of media, including books, comics, movies and video games. Many of them are preserved and available for free on BioMedia Project. Personally I'd recommend starting with the Mata Nui Online Game, as it serves as a good introduction to the story and is, in my opinion, one of the best pieces of Bionicle media of all time. I also highly recommend Cross-Wired Geeks' Biological Chronicle. It compiles books, comics and other official Bionicle media to give you the full Bionicle story!

As Bionicle sets are no longer produced by Lego, you're most likely to find the used sets on Bricklink or other online marketplaces. However, since most of the toys are about 2 decades old, your sets are likely to have loose joints or cracked pieces. If you want to build with Bionicle pieces without any risk of breaking them, you should check out Bricklink Studio software and the resources created for it by the Bionicle community.