The largest of the genus Heloderma and the largest lizard in North America, the fanged crater lizard (also known as the giant beaded lizard) can grow up to 1 meter (3.2 ft) in length and weigh as much as 6 kg. Fanged crater lizard populations are concentrated primarily in the Caparazón de Tortuga Crater and nearby Ludwig Cave System on the US-Mexico border and the surrounding area. Caparazón de Tortuga is neither an impact crater nor volcanic caldera. In actuality, the geological formation is a rather circular erosion cirque, similar in some fashion to the makhtesh found in the Near East. The circular depression is isolated by steep stone walls, except for a single small river draining to Rio Grande. The crater strangely devoid of large carnivoran mammals like coyotes or mountain lions. It is unclear whether mammalian predators are absent because of competition with the crater lizard or whether their absence allowed the crater lizard to grow to its current size. Sexual selection may have also been a factor. Regardless, the crater and its associated cave system is inhabited by many unique species not living outside the depression.

The crater lizard is colored primarily a dull black with orange and yellow stripes radiating from a single fire orange stripe running down the back. The typically solitary lizards mate during the late fall into early winter, and hatch during mid-spring. It feeds primarily on small to medium-sized animals such as the endemic beige cactus rat and peccaries, but will take carrion or eggs if it have the chance. This diet has led the lizard to have much more varied dentition than other Heloderms. While the teeth set in the front of its mouth are recurved and display the characteristic longitudinal grooves of the genus, its rear teeth are conical and dull; it is thought that this allows the crater lizard to better hold on to and subdue larger prey. In the 1880's, this led to biologist Horace Bromley initially identifying the fossilized tooth of a crater lizard as belonging to an ancient crocodilian. The fanged crater lizard would be properly described following the 1957 geological expedition to the Ludwig Caverns by Hank Scott and Arturo Ramos, accompanied by zoologist Terry Alvarez. This expedition also discovered several other species unique to the crater and cave system, most notably, the largest extant scorpion, the big-eyed cave scorpion, which can grow up to 50 cm in length.

The fanged crater lizard would receive popular notoriety just two years later in 1959, when several fanged crater lizards were let loose during a sock hop in the small town of Dead Gulch, Texas. It caused a few major injuries but thankfully no-one was hurt. Police arrived twenty minutes later and shot the lizards dead. To this day, they can be found at the local Dead Gulch Museum. It was assumed to have been transported and released as a prank by local teenagers. However, some currently believe it to have been the work of Colmillos de la Hidra.

While the lizard can be aggressive if angered, all recorded instances of injuries upon humans have occurred on account of the lizard defending itself. Indeed, the fanged crater lizard is a critically endangered species with only approximately 270 specimens in the wild, primarily due to poaching for skin and habitat loss, as well as culls originally organized by corrupt cattle baron and Dead Gulch mayor Enrique Rios III. The potential border wall proposed by Donald Trump would also have a negative impact on the Fanged Crater Lizard as the Caparazón de Tortuga Crater is situated on the border between New Mexico and Chihuahua. While current border fences extend along much of the surrounding area, the crater was left free in order to not impede the movements of several endangered species which live within it. The steep walls of the crater form enough of an effective natural impediment that the US border patrol has previously relied solely upon a virtual fence of cameras. However, prominent Republicans has decried this practice as valuing the lives of lizards over national security. Fortunately, other conservation and education efforts have paid off and have actually increased their numbers. It partially helps that it's been given a more positive public image through the popular franchise Gabby and Rex, which stars an anthropomorphic fanged crater lizard named Rex alongside the main protagonist Gabriela "Gabby" Jones.

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