Strictly speaking, a cow is a female member of any breed of domestic cattle, though the term is colloquially used to refer to both female and male cattle (bulls). Like humans, cows are native to the planet Earth.
In the universe of Earthworm Jim, cows are found on many different planets, and some breeds of cows are semi-sentient. Earthworm Jim has saved them many times, and the cows revere him as a god, "Brahman Brahma", since Jim can never say no to a bovine in need. Sadly, nobody else in the Earthworm Jim universe seems to treat cows with the same respect as Jim.
Recurring characters in the Earthworm Jim franchise, cows appear in every video game, and predominantly in the artwork to the games. Cows also appear in the comic book mini-series, and in the animated television series. In the latter two, they feature less prominently than in the games. One cow does land on Princess What's-Her-Name at the end of the pilot episode, just like in the end of the first game. In the animated television series, a cow always lands on a character right at the end of every episode, usually Jim.
In the early part of the first level, New Junk City, Earthworm Jim is forced to launch a cow into the stratosphere in order to progress forward. The trap, set up by Chuck, involves a lever system and a precariously hanging refrigerator. This brings up a screen saying "cow launched", and in the Xbox 360 version, unlocks the "Snot a Problem" achievement. This same unfortunate cow is subsequently seen flying by the screen, or flying by in the background, in various later stages. After defeating Queen Slug-for-a-Butt on Insectika in the final level, Jim rescues Princess What's-Her-Name which starts the end sequence. However, the cow from the beginning of the game lands on the princess. Although the cow is unharmed, and it continues to moo through the credits, the princess is squished. After the credits have rolled, Jim sheepishly takes her crown before slinking off.
Cows also feature predominately in Earthworm Jim 2. Two cows appear at the end of every level; the one on the left smiles a beaming grin, whilst the one on the right speaks, saying "well done." In some ports of the game, different inter-level screens could be seen, such as these two cows surfing.
One Earthworm Jim 2 level, Udderly Abducted, features dozens of cows. Jim has to save them from alien abduction, and take them to various milking shacks where their milk will raise a pulley system, allowing level progression. A large number of massive, insane-looking mutated cows with name tags are seen in the background of the abattoir of Totally Forked, a secret level later in the game.