Before infection/The Evil Dead
Ash's right hand was just that, his right hand, and remained on his arm before and during the events at the cabin.
After experiencing an hallucination of a still possessed Linda coming out of her grave her head lands on Ash's lap and takes him by surprise, this gives Linda the chance to bite into Ash's hand, causing Ash immense pain as he tried getting Linda off his hand, eventually managing to do so in the work-shed where Ash kills Linda for good with a chainsaw. Later on Ash has an encounter with his reflection in the mirror who begins to strangle Ash, Ash soon snapping out of it when he realizes he had been choking himself the whole time. The bite from Linda soon begins to take it's effect as Ash witnesses his hand turning and becoming possessed, and his hand begins to attack him, Ash is distraught at his hand becoming possessed as he screams "Give me back my hand!" His hand continues to attack him, by either bashing his head into the kitchen sink, or continuously breaking plates against his head. After Ash passed out, the hand was about to break another plate on his head, when it spotted a butcher knife, or cleaver, in other words. The Hand pulls itself and Ash (Because it is still connected to his arm) to the cleaver. Right before it reaches the cleaver, Ash stabs it with a kitchen knife. While saying "Who's laughing now?!" Ash notices the chainsaw on the floor, reaches for it, starts it up with his teeth, and then severed his hand. He covers the hand with a bucket and a pile of books (with "A Farewell to Arms" humorously being the top book). The hand however manages to escape, and Ash takes a few shots at it, trying to shoot it out of the wall before it causes more trouble, becoming annoyed when his own hand gives him the middle finger; Ash is unsuccessful in this feat and the hand isn't seen for a while.
Sometime after Annie and her group arrives the Hand makes it's presence known to the group as it fools Bobby Joe into thinking she was holding Jake's hand, and scares her out of the cabin and deep into the woods where she meets her death. Later as she recites passages from the Necronomicon Ex-Mortis in order to banish the Deadites the hand fatally stabs Annie in the back with the Kandarian Dagger, though she uses her last breathes to finish the passages and banish the Deadites.
At some unknown point Ruby Knowby had found and taken the hand, and when it begins moving again after 30 years this lets her know Ash is still alive. After meeting and teaming up with Amanda Fisher Ruby intends to use the hand to track Ash on his journey to stop the evil that he has unleashed. Eventually the hand manages to leave the two women and crawls it's way back to the Cabin. It is soon seen crawling behind the walls, though somehow it had started to grow an arm before it eventually grew a new body, becoming a brand new Evil Ash. While this Evil Ash looked identical and acted just like the original the hand however still retained it's rotted look, and helped Amanda realize she had been talking to a fake Ash, and during a fight with Evil Ash history repeats itself when the hand is once again chopped off at the wrist by Amanda, however it doesn't get very far as it is finally killed off when Amanda chops it into pieces.
After traveling back to 1982 and altering time Ash's right hand grows back and Pablo Simon Bolivar, who had recently been killed by the demonic being Baal, returns from the dead much to Ash's delight. However it's soon revealed that Pablo was in fact Baal wearing Pablo's skin, and Ash later on challenges Baal to a fair one on one fight, whoever ones gets their desire granted (Ash's being the Necronomicon and Baal to be sent back into the depths of Hell and for Pablo to truly be resurrected, while Baal's is to rule the world), during the fight Baal cheats and, in the guise of Chet Kaminski, uses a chainsaw to sever Ash's new hand. Once again losing his hand the hand also becomes a new Evil Hand and gives Ash the finger once again before crawling away somewhere in the cabin. It's not known what happens to this new Evil Hand afterwards, though it can be assumed it was killed when Ash won his fight against Baal and the entire cabin was burnt to the ground.
Beyond The Films and Television Series
2004-2013, 2016-Ongoing Army of Darkness Comics
Ash's hand returns in Ashes 2 Ashes when Ash and The Wiseman return to the Cabin to ensure that the Ash from the past goes to 1300 AD. Later in the story, the hand stabs The Wiseman in the back (similar to Annie Knowby) and attaches itself to a skeleton, resurrecting Evil Ash once more. The hand reappears in the Old School story-arc, where it turns on Professor Knowby's tape recorder, resurrecting those who died in the Cabin previously, such as Annie Knowby and Henrietta Knowby.
Ash's hand comes back to haunt Ash after eight years. It activates the tape recorder, and summons the deadites at the beginning of the game. It comes back when Ash returns to the past.
At some point, Ash possesses the hand and uses it to activate levers to get past a gate.
You got quite attached to your body and don't want to lose that bond. So you need to reintegrate it.. But it is fiercely fighting back and you gotta to choke it a little bit beforehand.