Nokturnus

"No mortal commands me... I obey only my own dark urge to reduce all to nothing."

- Nokturnus in Dragon Quest VI "Brutal bad-dream demon from another dimension. So strong that he makes Mortamor seem more like Snoretamore!"

- Dragon Quest IX Bestiary

Nokturnus (ダークドレアム, Dark Drium in the earliest Game Boy Dragon Quest Monsters games, Dark Dream in fan translations) is a notable figure and one of the most relentless and powerful villains in the Dragon Quest RPG videogame franchise. This dreadful figure presents himself as an entity with no master and with the sole desire of returning everything to nothingness.

He originated in Dragon Quest VI as an optional, more powerful super-boss and since then, has had many appearances in the saga. One of his most notable ones is in Dragon Quest Battle Road Victory, where he's the leader of all the final bosses up to Dragon Quest IX (and possibly of Dragon Quest X 's had it come out at the time).

Dragon Quest VI
Nokturnus is first encountered as the demon that the king of Castle Graceskull in the Dream World tries to summon in order to stop The Archfiend. Things don't go as planned; the brutal demon refuses to take orders from anyone and he ends up burning the whole castle. The heroes are returned to the Real World where the castle is already destroyed, and its tragic fate can be experienced again and again if the hero enters the well. The entire sequence is played as a flashback, since it had happened already before the game begins.

After beating the game once, an optional dungeon can be accessed in the large room in Alltrades Abbey. Upon traversing the dungeon, the player will find the offering room from Castle Graceskull, where you are given the option of completing the offering to summon Nokturnus and then fight him. Nokturnus is obviously much more powerful than any other enemy in the game, having more HP than the three forms of Mortamor combined and an assortment of hard-hitting spells and techniques. Upon being defeated, Nokturnus will comment on the player's capabilities and tell how many turns it took to defeat him, daring you to try to defeat him faster. If you manage to defeat him in 20 turns or less, an alternate ending is unlocked, where he congratulates the player and demonstrates his power by easily killing the final boss, Mortamor, with a single blow. Defeating him also gives the player a slim chance of earning a Liquid Metal Mind scroll (required to take on the Liquid Metal Slime vocation) if he has a thief in the active party.

Dragon Quest Battle Road Victory
Known to be the leader of all final bosses up to Dragon Quest IX. He could probably also have been the leader of Dragon Quest X's final boss, had it come out before this game.

Trivia
It appears that Terry holds a grudge this demon, or maybe Terry just enjoy to test his own power the most powerful foe he has known; this because the lone warrior was last seen summoning this demon at the end of the game. Also, Nokturnus is set to appear as DLC in Terry's Story in Dragon Quest Heroes.