Dan Garrett found the Scarab on an archeological dig. It became his symbol to fight crime as the Blue Beetle. It also gave him super strength, flight, and the ability to create lightning when he cried the word 'Khaji Da' out loud.
The Second Blue Beetle, Ted Kord was given the Scarab, however he was never able to use it. Shortly before his death, the wizard Shazam steals the Scarab from him seeing that it will soon fall into the hands of a great hero.
The Scarab later finds Jaime Reyes and embeds itself onto his spine. Jaime can access the full power of the Scarab to create a alien suit of armor. Jaime learns that the Scarab is actually a life form create by The Reach sent to Earth in order to conquer it. It was, however, unable to fulfill its mission because it was too damaged to fully take over its hosts body. It turns out that Khaji Da is the name of the Scarab.