Ein (アイン Ain?) is a Pembroke Welsh Corgi. He was known as a "data dog," meaning that his intelligence was greatly enhanced by a research facility. What exactly was done to him was not widely known. Ein became part of the Bebop crew and was a good friend of Edward.
Ein was modified in a laboratory until Abdul Hakim stole him intending to sell him. Hakim put him into a briefcase and escaped the facility. While setting up a rendezvous with the buyer, the briefcase was stolen by another thief unaware of its contents. The thief went to Animal Treasure hoping to cash in, but was caught by Spike Spiegel, who was looking for Hakim. The shop owner was forced to open the briefcase and Ein was revealed. Spike left, thinking it wasn't related to Hakim, but then Hakim soon appeared to confront the thief. He tried to grab Ein, but Ein jumped and caused a commotion which freed other animals in the shop. Hakim ran after Ein with Spike in pursuit, drawn to the commotion. Ein was able to lose Hakim and get close to Spike, who he immediately trusted, by enticing Hakim to jump onto a boat while Ein slowed Spike down while he chased after him.
Spike walked Ein later as bait for Hakim, only for Ein to be drawn to a dog whistle from the research scientists who were still looking for him. Hakim saw Ein run by, and was able to grab him, rendering him unconscious, and drive away in a stolen car. Ein woke up, however, and interfered with Hakim's driving as he avoided Spike in the Swordfish II. Ein jumped out of the car and was fortunately saved by Spike. With Hakim captured, Ein was then part of the crew, despite Spike's dislike of animals. 
Ein had first noticed the Fridge Monster while on the way to Mars. When he saw Jet in the storage bay after having been bitten, he growled at the fridge, however, Spike and Faye thought he was growling at a rat, and discounted him. Ein went with Ed to look for the creature later, and he left her to explore, but was subdued. Spike found his body and rescued him from another attack. 
When the Bebop crashed on Io, Ein went with Ed to look for food. They eventually encountered Domino Walker, who dropped mushrooms as he ran away from Shaft. Ein quickly ate one and was instantly affected by its hallucinogenic properties. He later observed with Ed the effects of the mushrooms on the rest of the crew. Later, he got on Ed's back as she drove a scooter out to find Walker. They chased him to a train, and Ed jumped onto the train and forced Walker to drop one of his bags, beating Shaft to him. The train stopped due to a cow on the tracks, which Ein thanked in his own barking language. The cow, in its own language of moos, said "oh, don't mention it." 
While Faye had left the Bebop to avoid a package she assumed was from collectors, she contacted the ship to see Ein answer the call. She thought nothing of his ability to do that, and asked if someone else was there (who could talk). 
When Meifa Pu-Zi was on the Bebop trying to figure out the mystery of the sunstone, Ein figured it out and gestured with it to Meifa's Luopan. Ed put it in and, indeed, it interacted with the stone. 
When the crew was investigating Scratch, Jet Black put on a Brain Dream in order to get some information. Ein looked at the screen and realized Jet was in trouble. He jumped over to him and bit him, hard, in order to wake him up and take the device off. Jet then got the idea to let Ein try it. To Ed's surprise, Ein navigated the menus faster than a person and hacked into the organization's computer. They found out where Rosny Spanngen was. 
When the crew was investigating Vincent Volaju, Ein deduced he was the culprit long before anyone else suspects him. He barked at a picture of him next to other Mars army members. Edward trusted Ein's instincts, but Faye needed more convincing. 
Ein left the crew when he sensed Ed was leaving the ship for good, as she found her father. Ein hesitated after leaving the ship, but decided to go to Ed. Ed made sure Ein wanted to come with her, encouraging him to go back. Ein stayed, and Ed led the way. 
In the preview for Wild Horses, Ein manages to speak the session's name. Spike hears this and is shocked, but seems to brush it off. Being a preview, it's likely this is not considered canonical.
Despite Ein's enhanced intelligence, he remained incapable of speaking (other than barking like any dog). Because of this, his intelligence largely goes unnoticed. Ed came to understand Ein through his body language and barking. Ein also barks once for "yes" and twice for "no".
- All of Ein's vocalizations were done by a Cardigan Welsh Corgi named Jack, owned by the show's producer Kazuhiko Ikeguchi.
- Japanese voice actor: Kōichi Yamadera 
- Given the dog's highly intelligent nature, the name "Ein" is likely short for "Einstein".
- Ein's popularity on the show has resulted in an upsurge of Welsh Corgi's named "Ein."
- Another possibility is that the name is the German translation of "one", in the meaning of him being considered a he or an it. It can also be interpreted that, in Japanese, the way dogs bark is "wan" (ワン, pronounced the same as "one"), hence the name "Ein".
- An allusion to Ein appears in the RoosterTeeth series RWBY through the character of Zwei (a dog of similar breed and intelligence). Eins is the German word for "one" while Zwei is German for "two".