Ekans is a purple, serpentine Pokémon. 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 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. It was also shown in the second movie to possess some swimming abilities. Its former signature move is Glare.
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 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 the manga Magical Pokémon Journey. Led by Arbok, they are originally antagonists, but later befriend the main characters when Arbok gets a crush on Wigglytuff.
Ekans and Goldeen have never been scanned with a Pokédex in the anime, despite having made their debut in the second episode, making them the Pokémon with the most episodes aired since their debut episode without them receiving a Pokédex entry.
Ekans appears to be based on a boa and rattlesnake, and its facial markings resemble an Indian cobra's hood. However, its lack of teeth, ability to swallow large prey, preying on Pokémon eggs, and reaction to threats are more akin to an egg-eating snake. The yellow band around its neck may refer to the ring-necked snake. Ekans and Arbok may also be inspired by the legendary basilisk since they were originally the only Pokémon to learn Glare. The basilisk was said to be a poisonous, serpentine dragon that would kill people with its stare, which may explain Ekans's place in the Dragon Egg Group.