In The 1984 movie, he and Isaac and the other kids killed the adults in the town of Gatlin. Three years later he makes very strict rules, like not letting the kids draw, play boardgames or listening to their record players. He kills one of the kids, Joseph, by slitting his throat for trying to escape Galtin and getting help. He later on double-crossed Isaac after many demands by placing him on the cross. Later on at Night, after Burt saves Vicky, Malachai meets his fate after Isaac gets possessed by "He who Walks Behind the Rows" as Isaac grabs Malachai's neck and breaks it.
In the 2009 remake (which follows Stephen King's Children of the Corn in every detail), Malachai was first introduced along with Isaac after seeing Burt and Vicky drove off with Joseph's Body (who was killed by Malachai while escaping Gatlin to get help). Then He is seen later at the cornfield witnessing Isaac's speech. Then later on he and the boys surrounds Vicky's car, and he answers to Vicky's question by saying " We come to give you peace". He then grabs her out of her car and stabs her in the neck killing her. When Burt came out of the church, Malachai lits a cigarette on fire from his knife and throws it in the gaseline ( which was dripping from the car), blowing it up.
Then he and Isaac demand the children to hunt down and kill Burt. While in the cornfield, he meets a young boy named Nadham who believes he's the next candidate for becoming the preacher boy after Isaac reaches the age of favor. Nadham told Malachai that he saw "He who Walks Behind the Rows". The next day Isaac said the sacrifice of Vicky displeased " He who Walks Behind the Rows" and they failed to kill Burt. In reality Burt was actually killed by the demon of the cornfield and ended up becoming a scarecrow. Isaac said that the age of favor was lowered from 19 to 18. Isaac also said that the children who turn 18 must go into the cornfield and walk with "He who Walks Behind the Rows" and keep walking with him. Later on that night, before Malachai walks in the cornfield with the other eighteen-year-old teens, he says goodbye to his girlfriend Ruth (who is pregnant with their child) and enter into the cornfield.