Gabara gets its name from Ichiro's bully, who is also called Gabara.
The audio commentary for Classic Media's 2008 DVD release of All Monsters Attack humorously compares Gabara to a bipedal cat with car engine problems. Although not based on any real animal, living or extinct, Gabara is very similar to—and more than likely based on—the Oni of Japanese mythology and folklore. His costume design is very reminiscent of these demonic ogre / troll-like beings, further mixing the turquoise scales of a reptile with orange, cat-like fur. He also has three horns on his head, again much like the Oni, whose horns varied between one-to-three on average.
Gabara's ability to electrocute things on contact is possibly a reference to Oni lore, as they too were sometimes associated with the natural forces of lighting and thunder.
Just as All Monsters Attack is one of the more distinctive entries in the Godzilla canon, Gabara is very unique amongst the other Toho monsters. It seems that Gabara exists entirely inside the dreams of lead child character Ichiro.
In the context of the film, Gabara is a resident of Ichiro's imaginary Monster Island, and a constant tormentor to the much smaller Minilla, inspired by Ichiro's own real life problems with bullies around his neighborhood. After receiving combat training from his father Godzilla, and extra assistance from the human protagonist, Minilla does successfully challenge it. Finally, Gabara was confronted by Godzilla himself and got beat up. Gabara retreated after Godzilla performed Seoi nage on it.
Despite the film's overuse of stock footage, Gabara was the only original monster created for the film, along with newly filmed fight scenes and effects.
Gabara did not make any further appearances in the Showa Godzilla films, but Gabara did later appear in a similar series called Go! Godman. It's unclear if this means Gabara exists outside of Ichiro's dreams, that Godman's adventures (or at least that episode) take place within them, or if the two are unrelated. In this series, Gabara's skin tone is changed to a dark, greenish-blue colour, and he lacks his trademark ginger hair. Due to mild deterioration of the suit's face, his eyes appear to take on a more confused or surprised expression. This damage was repaired in time for the show's followup, Go! Greenman.
Gabara returned in the fourteenth episode of the giant hero television series, Go! Greenman, a followup series to Go! Godman. In the show, he could throw explosives and engulf children into his body. This was shown when he engulfed an innocent boy before being repelled by Greenman. Gabara's suit underwent extensive repairs, as his skin is now a lighter shade of green, and the plates on his torso are almost gold in colour.
Gabara can channel energy through his body in the form of electricity. He can then either fire this from his Power Horn or channel it into his arms, and electrify anything he touches.
In Go! Greenman, Gabara could throw small, but powerful, handheld explosives and engulf children into his body.
In a 1990's Monstervision commercial for Turner Network Television (TNT), which used Godzilla film footage with Blue Oyster Cult's related song in a music video-like fashion, Gabara is incorrectly referred to as "Baragon."
In the Simpsons episode "30 minutes over Tokyo,' in the end Gamera, Rodan, Mothra and Godzilla are attacking the Simpsons and Gabara's laugh-like roar is heard.
Within the context of the film, Gabara is a representation within the dreams of Ichiro, the main character, of a schoolyard bully of the same name. Similarly, Ichiro is represented by Minilla, Godzilla's son. After Godzilla defends his son in Ichiro's dreams, Ichiro is able to overcome his fears and confront the real Gabara.
Gabara is the one of only two monsters in the Toho universe that exists only in dreams, the other being the Maneater; that is to say, they do not exist in the "real" world like Toho's other kaiju.
Gabara is probably an imaginative take on the Oni, an ogre-like race in Japanese mythology. Confirmed kaiju that are Oni can often be seen in the Ultraman franchise, with characters like Oni-On, from episode 27 of Ultraman Leo, and Sakunaoni from episode 16 of Ultraman Tiga. In the Tokusatsu series Go! Godman, Gejiba is another example of a kaiju based on Oni produced by Toho.