Blue Beetle is the name shared by three superheroes from the DC multiverse.
Blue Beetle (Dan Garrett)
Rookie police officer Dan Garrett was given doses of the super-power-endowing Vitamin 2-X and a bulletproof costume by Dr. Franz to battle crime as a superhero. He wore a revolver (and was known to shoot criminals dead with it), drove vehicles like the Beetlemobile and Beetlebird, and used blue beetles as his signal and calling card. He briefly had a sidekick, Sparky, who later aided his mentor as a non-costumed civilian. In addition to a successful career fighting crime in the U.S. during the 1940s, the Blue Beetle also battled the Axis powers, sometimes working with Samson and the Flame as the Big Three. The Blue Beetle was ultimately slain by a mad scientist's bomb.
Blue Beetle (Dr. Dan Garrett)
Archaeologist Dr. Dan Garrett found a mystic blue scarab in the tomb of the Pharaoh Kha-ef-re. He discovered that when he held it and said the words "Kaji dha," he would be transformed into the superheroic Blue Beetle, able to redirect his internal energies to fly, exhibit superhuman strength, fire blasts of lightning, fly, or use telescopic vision. He fought crime for a short time, before finally deciding to settle down and focus on his life as Dr. Dan Garrett.
However, some time later, he was summoned Pago Island to help his friend Ted Kord, whose uncle Jarvis Kord planned to use an army of androids to conquer the world. Garrett was forced to become the Blue Beetle, and although he did destroy Jarvis' machines, he and Jarvis were both mortally wounded. Garrett tried to pass on the scarab and identity of Blue Beetle to Ted Kord, but was buried when Jarvis' underground lab collapsed. Despite not having the scarab, Kord became the new Blue Beetle to honor his friend.
A year or so later, Kord battled the villainous Carapax on Pago Island, and the destruction of their battle caused Garrett to reawaken. However, his weakened mind was seized by a malevolent alien intelligence inside the blue scarab. Garrett was filled with a jealous rage against the friend who had "stolen" his identity, and returned to Hub City to attack Kord. During their battle, Garrett became aware of what was happening: in a battle of wills with the alien mind in the scarab, Garrett shattered the scarab before truly dying.
Blue Beetle (Ted Kord)
Ted Kord was the inheritor of Kord Industries and the legacy of Dr. Dan Garrett, the previous Blue Beetle. Without the super-powered scarab of the original, Ted Kord became a hero using intense physical training and a variety of inventions, including his hovering Bug vehicle. He fought crime in his hometown of Hub City, and later joined Maxwell Lord's new Justice League after the Legends crisis.
Blue Beetle stuck with several incarnations of the League, becoming friends with Booster Gold and facing many threats with them. During the Justice League America battle with Doomsday, Kord was badly wounded and wound up in a coma for some time, finally emerging in time to save the League from Doctor Destiny. He left the League after Zero Hour and joined "Extreme Justice" for a short time, as well as the LAW. However, after discovering he had a heart condition, he retired to focus on Kord Industries. He was lured out of retirement to join Maxwell Lord's "Super Buddies" team, until a string of thefts from his company led him to Maxwell Lord's true plans- to wipe the world clean of superbeings. Refusing to join Lord in his crusade, he was shot dead.
Prior to the Crisis on Infinite Earths, Kord was a native of Earth-4. During the Crisis proper he inexplicably had (but didn't use) the scarab owned by Dr. Garrett, and it only served as a defensive device.
Blue Beetle (Jaime Reyes)
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Although DC owns the rights to the first (Golden Age) Blue Beetle, and discussed the character in the Cosmic Cards trading card set, he never actually appeared in any DC Comics. The Blue Beetle's run in Charlton's Americomics established that all three Blue Beetles were in the same universe, so it seems safe to assume he was a native of Earth-4 who ceased to exist after the Crisis on Infinite Earths.