Ekans is a purple, serpentinePokémon. Its eyes, underbelly, the thick stripe around its neck, and rattle are yellow. Ekans has three pairs of black lines encircling its body, as well as another line that connects to each slit-pupiled eye and curves toward its nose. Its large mouth has a round, pink tongue and no visible teeth. While painful, a newborn Ekans's bite is not venomous. This Pokémon grows longer with age.
Ekans lives in grassy savannas and plains, where it moves stealthily through grass. It can also be found in forests and desolate wastelands, where it preys on Eggs from Pidgey and Spearow nests, but will strike other prey from behind. By flicking its tongue out, it is able to detect danger and the scent of prey. Its jaw can detach to swallow large prey, but such a meal can make Ekans too heavy to move or become stuck and cause it to faint. It wraps itself around tree branches at night to rest. If not in a tree, it will coil itself up—a position in which it can defend itself from all directions. In the second movie, it is revealed to possess some swimming abilities. In Generation I, Glare was its signature move.
Ekans was part of Team Meanies in Pokémon Mystery Dungeon: Team Go-Getters Out of the Gate!. Gengar commanded the Poisonous Snake Pokémon to eat all of the Berries Team Go-Getters had collected. At one point, Ekans was incorrectly referred to as Arbok by Gengar. While this was an intentional error that Ekans rebuked in the original version (due to the similarities between the Japanese names), this came across as a general mistake in the dub and was corrected in reruns of the episode.
A pair of Ekans known as the Ekans Brothers are part of the supporting cast in Magical Pokémon Journey. Led by Arbok, they are originally antagonists, but later befriend the main characters when Arbok gets a crush on Wigglytuff.
Ekans has never been scanned with a Pokédex in the anime, despite debuting in the second episode of the original series. As such, this makes it the Pokémon with the most episodes aired after its debut without it getting a Pokédex entry.
Ekans seems to be based on various snakes. Its venomous bite and tail rattle are similar to a rattlesnake, while its lack of visible teeth and diet of eggs are similar to an egg-eating snake. The single yellow stripe around its neck is reminiscent of the ring-necked snake, and the line connecting its eyes is reminiscent of the marking on the back of the Indian cobra's hood. The fact that it is in the Dragon Egg Group and its ability to learn Glare may be a reference to the legendary basilisk, a venomous, serpentine dragon said to be able to kill people with its stare.