The main story of Assassin's Creed takes place in 2012; Desmond Miles, a bartender, has been kidnapped by the fictional company Abstergo Industries in order to use as a test subject in the "Animus," a device that can recall ancestral memories buried in the user's DNA. Abstergo has Desmond use the device to recall the role of Altaïr ibn La-Ahad (الطائر ابن لا أحد , Arabic, "The Flying Eagle, Son of None"), one of Desmond's ancestors, in the "Assassin Brotherhood" during 1191 as part of the Third Crusade in the Holy Land. Desmond at first has trouble adjusting to the device, but eventually is able to relive Altaïr's exploits over the next several days. Much of the core game is then presented from Altaïr's point-of-view as seen by Desmond, though at times interrupted by glitches resulting from the Animus.
At the start of the memories, Altaïr is shown attempting to retrieve a "Piece of Eden", a strange artifact, from Solomon's Temple with the help of other assassins, but is stopped by Robert IV de Sablé, a member of the Knights Templar and sworn enemies of the assassins. Altaïr breaks all three codes of the Assassin's Creed to attempt to kill de Sablé, but fails; upon returning to the Brotherhood, Al Mualim ("The teacher"), leader of the Assassins, demotes Altaïr to an initiate, giving him another chance to rise through the ranks of the Brotherhood. To this end, Al Mualim assigns Altaïr the task of assassinating nine key figures across the Holy Land in Jerusalem, Acre, and Damascus, in order to attempt to bring peace between the Crusaders and Muslim forces. Altaïr methodically completes each task, learning that each target is connected to Robert and the Templars and share their mysterious goals. Altaïr's final target, de Sablé, reveals in his dying words that Al Mualim is himself a member of the Knights Templar, and used Altaïr to kill the other members so he could keep the treasure for himself. Altaïr quickly returns to Masyaf to accost his master. Al Mualim reveals the truth; the Piece of Eden creates illusions, and he denounces religion and other seemingly supernatural events as illusions caused by it. He then states his intention to use the artifact to compel mankind into a brainwashed state and so bring an end to conflict. Altaïr attempts to kill his former master, but Al Mualim uses the Piece of Eden to warp Altaïr's vision. Altaïr is eventually able to see through the deception and kill Al Mualim, recovering the artifact. As he does, the Piece of Eden activates, showing a holographic view of the world with numerous locations marked across the globe.
After this memory is completed, Desmond is brought out of the Animus, his purpose seemingly completed. He learns that Abstergo are part of the modern-day Templars and have been using Desmond's memories of Altaïr to discover the holographic map in order to find more artifacts that can be used towards the Templars' mission. Desmond further learns that the modern-day equivalent of the Assassin Brotherhood has tried, and seems to have failed in rescuing him before that knowledge was gained. At the end of the game, Desmond is left alone in the locked Animus room, no longer needed, but finds that through his experience with Altaïr's memories he can see hidden messages painted about the room from a range of religions and cultures that portend the end of the world.
Assassin's Creed is a third-person stealth game in which the player primarily assumes the role of Altaïr as experienced by Desmond. The primary goal of the game is to carry out a series of assassinations ordered by Al Mualim. To achieve this goal, the player must travel from the Brotherhood's headquarters in Masyaf, across the terrain of the Holy Land known as the Kingdom to one of three cities, Jerusalem, Acre, or Damascus, to find the Brotherhood agent in that city. There, the agent, in addition to providing a safe house, gives the player minimal knowledge about the target, and requires them to perform additional intelligence gathering missions prior to attempting the assassination. These missions include eavesdropping, interrogation, pickpocketing, and completing tasks for informers and fellow assassins. Additionally, the player may take part in any number of side objectives, including climbing tall towers to map out the city, and saving citizens who are being threatened or harassed by the city guards. There are also various side quests that do not advance the plot such as hunting down and killing Templars and flag collecting. After completing each set of assassinations, the player is returned back to the Brotherhood and rewarded with a better weapon and then given another set of targets, with the player free to select the order of their targets.
The player is made aware of how noticeable Altaïr is to enemy guards as well as the current state of alert in the local area via an alertness level meter. To perform many of the assassinations and other tasks, the player must consider the use of commands distinguished by its type of profile. Low profile commands allow Altaïr to blend into nearby crowds, gently pass by other citizens, or other non-threatening tasks that can be used to hide and reduce the alertness level; the player can also use Altaïr's retractable blade to attempt low profile assassinations. High profile commands are more noticeable, and include running, scaling the sides of buildings to climb to higher vantage points, and attacking foes; performing these actions at certain times may raise the local area's awareness level. Once the area is at high alert, the crowds will run and scatter while guards will attempt to chase and bring down Altaïr; in order to reduce the alert level, the player must control Altaïr as to break the guards' line of sight and then find a hiding space such as a haystack or rooftop garden, or blend in with the citizens or wandering scholars. Should the player be unable to escape the guards, they may fight back using a number of swordplay maneuvers.
The player's health is described as the level of synchronization between Desmond and Altaïr's memories; should Altaïr take damage, some amount of synchronization is lost, and if all synchronization is lost, the current memory that Desmond is experiencing will be restarted at the last checkpoint. When the synchronization bar is full, the player has the additional option to use "eagle vision" which allows the computer-rendered memory to highlight all visible characters in colors corresponding to whether they are friend or foe or even the target of their assassination. Due to Altaïr's memories being rendered by the computer of the Animus project, the player may experience "glitches" in the rendering of the historical world, which may help the player to identify targets, or can be used to alter the viewpoint during in-game scripted scenes should the player react fast enough when they appear.
On October 22, 2007, in an IGN Australia interview with Patrice Desilets mentioned that the lead character's climbing and running were done by "Alex and Richard – the same guys from Prince of Persia".
Altaïr (meaning "The Flying One" in Arabic) is a star in the Northern Sky in the constellation of Aquila ("eagle" in Latin); this ties in well with the white eagle seen in the trailer, that is shown flying over the city of Acre, and lands on the bell tower Altaïr himself is standing on. To complete the theme the Assassin's clothes consist of white flowing robes. His hood also has a hook on the end and his lower robe features a stream on each side, therefore making Altaïr's shadow in air look like an eagle. According to Ubisoft Altaïr is not religious but rather spiritual and is the son of a Christian mother and Muslim father. It is also stated that in events before the start of the game, there is an initiation where Altaïr's left ring finger is cut off, so that he is no longer a novice, but an assassin. This procedure provides for the hidden blade to extend from under Altaïr's forearm.
The Nintendo DS prequel, Assassin's Creed: Altaïr's Chronicles, was released on February 5, 2008.
On August 26, 2007, an 11-minute demo of Assassin's Creed was shown at the Penny Arcade expo. The level that was shown was the same as in the E3 demo; however, a different path was taken to reach the target. At the end of the demo, a conversation between Altaïr and the head of the Assassin's bureau in Jerusalem called Malik was shown.
There is no demo available for Assassin's Creed over Xbox Live, the Playstation Network, or PC.
A pirated version of the game has been in existence since late February 2008 – more than a month before its expected release. According to Ubisoft a bug was purposely inserted into the pre-release version of the game by the publisher itself to unpredictably crash the game and prevent completion as a security measure, though players were able to use extra content available on the internet to bypass it. The pirated version of Assassin's Creed was one of the most popular titles for piracy during the first week of March 2008. The presence of the bug and performance of the pirated version of the game was believed by Ubisoft to lead to "irreparable harm" for the game and resulted in low retail sales; NPD Group reports that 40,000 copies of the PC title were sold in United States in July, while more than 700,000 copies were illegally downloaded according to Ubisoft. In July 2008, Ubisoft sued disc manufacturer Optical Experts Manufacturing, believing the company to be the source of the leak, citing poor security procedures that allowed an employee to leave with a copy of the game.
Assassin's Creed has received generally positive reviews, although several publications such as Eurogamer, while still awarding the game decent scores, pointed out a number of significant shortcomings. Eurogamer stated that the gameplay "never evolves and ultimately becomes a bit boring, and quite amazingly repetitive. In Andrew P.'s review for EGM(Kage), he writes that the game features "a challenging parkour path of escape… Famitsu awarded the Xbox 360 version of Assassin's Creed a 36 (9, 9, 9, 9), while the PS3 version received a 37 (10, 8, 9, 10) out of 40, positively citing the story, presentation, and acrobatics, while criticizing the one button combat, map layout, and camera problems. Game Informer awarded Assassin's Creed a 9.5 out of 10, praising the control scheme, replay value, and intriguing story, but expressing frustration over the "repetitive" information gathering missions. On the The Hotlist on ESPNEWS, ESPN's Aaron Boulding called the game's concept of social stealth "fairly original" and added, "Visually, the developers nailed it. GameTrailers similarly praised the story (giving a 9.7 score to its story), and also cited repetitive gameplay and "moronic" AI as somewhat stifling its potential. The game also received a 10 out of 10 from GamesRadar, and has a Metacritic score of 81. According to GamePro, Assassin's Creed is one of the "finest gaming experiences ever created" if you are willing to be "patient" due to the lack of fast-paced action.
Ubisoft announced that the game has sold more than 3.46 million copies as of March 1, 2008, exceeding their initial expectations and prompting the company to raise their sales outlook.
Ben Croshaw of Zero Punctuation gave it a positive review, praising the free roaming aspect, assassinations, and overall uniqueness of the game while criticising the combat and the lengthy cutscenes. In a later review for Oblivion, he again praised it, describing it as "immersive".
The award nominations and wins after release included:
Assassin's Creed has greatly outstripped Ubisoft's sales expectations and currently ranks among the top two or three best-selling games for the Playstation 3 computer entertainment system and Xbox360 video game and entertainment system in the vast majority of geographical regions. In less than four weeks Assassin's Creed recorded more than two and a half million units in sell-through sales worldwide, and is the fastest-selling new video game intellectual property ever in the U.S. Consequently, Ubisoft now forecasts that it will sell a minimum of five million units of the game in 2007–08 compared with its previous estimate of approximately three million.