Necessary Evil

Villains who can actually serve very important purposes and need to be kept alive, imprisoned, or simply kept around. No matter how sadistic, bloodthirsty, cruel, or even how much they are hated, these villains cannot be destroyed/killed or something terrible can happen. These characters are similar to Virtually Resourceful characters, but are obviously opposed to their alignment. These characters are usually created to keep the story relatively three-dimensional.

Perfect Examples of Pure Evil Villains are:

John Doe From Se7en: The Serial Killer had a tragic past due to his Abusive Mother,Her Abuse to him was the Main Reason he started his killings as an adult and as he used the Seven Deadly Sins as His Motives.

Michael Myers From Halloween: Before Attempting to kill his younger sister, The reason why Michael killed his sister was she rather hang out with her boyfriend rather then taking him out trick or treating. Also Dr. Terence Wynn Placed the curse on him into killing his entire family.

Commander Vic Hoskins From Jurassic World: Victor Thinks the raptors and Indominus rex are a powerful weapon to the Warfares and that he tried to hunt down the Indominus rex.

The Fallen From Transformers: The Fallen and his Seven Brothers were Creating a place called Star Harvesters,before Betraying his brothers and stealing the Matrix and activating the machine and attempted to wipe out all of humanity.

Lord Voldemort From Harry Potter: Tom Riddle grew up in an orphanage after his parents death and was educated to Hogwarts school from 1938 to 1945 before attempting to open the Chamber of secrets.

Freddy Krueger From A Nightmare on Elm Street: Freddy was sent to orphanage to orphanage after his mother's death and was taken in by a severe Alcoholic who is (Indirectly) Responsible for The murders of The death of the springwood children.

Villains Who Qualify

1. Some Anti-Villains with the intent to help the hero or to save a large number of people. Often,these characters are Considered Anti-Heroes. (Examples: Vegeta helps Goku and the other Z-Fighters protect the universe from threats,although initially doing so out of a desire to have his own shot at killing Goku; The Punisher fights off and defeats other super villains.
2. Villains who are keeping a much worse evil at bay. (Examples: Galctus keeps Abrades, a being able to destroy universes, out of the Marvel Universe; the Lich King keeps the Scourge from becoming an even greater threat to Azeroth; The Seven Deities, while seeking a new world order, protect Gaea from the Gohma Vlitra; while the remnants of the US Armed Forces in Last of us, despite running the quarantine zones as police states, genuinely protect the inhabitants from the Infected and attempt to help and be friendly with civilians whenever they can; Anna Morgan, Whilst depicted as an abusive and mentally disturbed Mother, keeps her adoptive daughter Samara Morgan from continuing her torment and killing spree).