That was my holocron. I crafted it so long ago, when foolish pride still crept about in my mind. Study its secrets with caution, lest the same pride take root in your own mind, child.
—Lord Karros to the Jedi Apostate
Karros's holocron was a Sith holocron crafted by the Pureblood Sith Lord Karros as a way to store his greatest writings for future use. Constructed of an unknown black material, similar to the metal cortosis in some respects, the pyramidal holocron shown with an eerie red glow, as was customary with Sith holocrons, even after many millenia of neglect.
After Karros's death, the holocron and its contents passed to his followers, the Karrossi, who studied its knowledge and eventually buried the device in their teacher's tomb. There it lay for many millenia until a hapless Jedi Revanchist named Suri Sunrunner entered the tomb and made contact with the Force ghost of Karros. With his approval, Sunrunner opened the sarcophagus and took with her the holocron and his lightsaber.