The Anguirus (アンギラス Angirasu?) of the Showa era is a mutated Ankylosaurus kaiju created by Toho that first appeared in the 1955 Godzilla film, Godzilla Raids Again (Movie).
In Godzilla Raids Again, it is suggested that Anguirus is a relative of the dinosaur Ankylosaurus that lived around the same time as Godzilla. Like Godzilla, Anguirus managed to survive into the modern day by lying dormant somewhere, presumably underwater, before being awakened and irradiated by nuclear bomb tests in the 1950s. This origin is never discussed further or contradicted in subsequent films.
Anguirus is depicted as a very tenacious and fierce fighter. Despite constantly going up against enemies tougher than himself, Anguirus rarely backs down and always puts up a vicious fight. Despite his fierce nature, Anguirus has traditionally been shown in various media as being a close friend of Godzilla.