"Killer" is a series of invisible video games developed by IO interactive, a Danish company. It was previously released by Eidos Interactive and square Enix. IO interactive has been a subsidiary of square Enix until 2017, when square Enix began to find sellers for the studio, IO interactive completed the management acquisition in June 2017, regained its independent status and retained the right of killer. This series of products can be used on Microsoft Windows. And several video game consoles, including PlayStation 2, Xbox, GameCube, PlayStation 3, Xbox 360, PlayStation vita, PlayStation 4 and Xbox one. The franchise also includes two novels and a graphic novel: the killer: inside the enemy by William C. Dietz, the killer: curse by Raymond Benson, and Agent 47: the birth of the killer.

The 2007 film adaptation (largely based on the game's storyline) received negative reviews but achieved economic success. Another film, "killer: Agent 47," was released in 2015, but received negative reviews.

The story revolves around Agent 47, an agent assassin whose impeccable record makes him in high demand among the rich and the elite. The first original screenwriter was Morten Iversen, who wrote scripts for "killer: Code 47" and "Killer 2: Silent Assassin.". He also contributed to "killer: contract" and "killer: blood money". These games combine orchestral and electronic scores created by Jesper Kyd. The fifth part of the series, "killer: pardon," was released on November 20, 2012. Meanwhile, derivatives for PCs, PlayStation 3 and Xbox 360 are also known as "killer: Sniper challenge.". For mobile phones and tablets, the derivative game developed by square Enix Montreal was released as a turn based strategy game called hitman go. Another game released for the mobile phone, killer: sniper, consists of a first person sniper game. The sixth game, killer, was released in fashion, with the first episode in March 2016 and the last in December 2016. The seventh game, Killer 2, was released in November 2018.

The killer series allows players to use guns, melee weapons or 47 kinds of regular items (such as shovel, fireplace game player, billiard bar, etc.) to kill targets (or non targets) in many ways. In hitman: contracts, there is more than one way to kill a melee weapon, such as a knife, including a front stab, a horizontal throat cut, a frontal slash, repeated stabs under the chest or a blade pushed into the carotid artery.

47 there are also garrote or fiber threads. Fiber optic cable is specially made for stranding, with enhanced handle. In carrying out every task, he will take it with him, even if all his weapons are taken away. It is also one of the few weapons that can bypass metal detectors.

To achieve the ideal "Silent Assassin" level, 47 people are required to kill only their assigned targets, with little or no other NPCs. For this reason, there are tranquilizer syringes or chloroform in "Assassin 2: Silent Assassin" (unlike syringes, which only have a temporary dose-dependent effect), so 47 innocent people may lose the ability to take items or clothing from them and hurt them, so it does not affect players in the final ranking. In blood money, the function of adding sedatives to food and drink is added to avoid direct confrontation. Blood money also introduces the option of using smaller weapons to hold any NPC hostage and use it as a human shield, and allows players to use guns to keep the hostage unconscious, thus saving players' food or sedatives. chair. In some tasks, if you can make a murder look like an accidental death (using the accident system introduced in blood money), some murders are not counted as hits, but as accidents. Any civilian or armed person killed by a witness will be treated as a witness and will damage the player's team if they are alive or warn nearby guards. However, if someone (target or civilian) dies as a result of an accident, it does not matter whether there is a witness. A 47 year old can choose to kill a witness before he reaches the guard, but unless he accidentally kills him, unnecessary murders will still be counted in his rank. Witnesses also included anyone who saw 47 people posing or holding weapons. In the game before bloody money, the only consequence of having criminal witnesses was that they would look for police / guards and trigger an alarm.

There are task specific options for specific levels of goals. Famous examples include locking the target in the sauna to stimulate a heart attack and lead to cardiac arrest, poisoning a meal (which has become more common in blood money), camouflage of 47 doctors, destruction of surgery, replacement of the prop Mauser c96 pistol, a real opera rehearsal, resulting in the actor accidentally killing the target, and the stage fireworks explosion and fire.

In most cases, requirement 47 also hides the bodies of victims killed or unconscious to avoid any unwanted alarms, or if this is the desired effect, 47 can leave the bodies of victims in a wide space for all to see.

Agent 47: a genetically engineered assassin made from the recombinant DNA of five of the world's most dangerous criminals. The fact that DNA comes from multiple races allows 47 people in most parts of the world to somehow fuse, or at least not seem immediately suspicious and inappropriate. His name comes from the last two digits of the bar code on the back of his head - 640509-040147. According to Jacob Andersen, chief designer of hitman 2: Silent Assassin, Agent 47 changed from a "mean, furry old guy" to someone with "high-tech glasses" before using the current design. More inspiration comes from "comic books, Hong Kong Films" and other similar media. According to rasmus H? According to jengaard, the idea of human cloning was decided by the man who created it, which aroused the interest of the Hitler team. H？ Jengaard came up with the idea of creating a "final Assassin" by cloning "evolved with characters before completing the first killer game.". So far, David Bateson (David Bateson) has published 47 songs in every "killer.".