Eagle Vision is a signature ability of the Brotherhood of Assassins in the Assassin's Creed franchise, the ability of an Assassin to scan the world around them and see otherwise invisible signs and symbols, and to tell at a glance what a person's intentions towards them are:
- Hostile people who would oppose the Assassin, even if they are not aware that that person is an Assassin yet, glow with an ominous red colour.
- Friendly people who would support the Assassin, whether it's to defend them in combat or just lend them their talents in exchange for a small fee, glow a bright blue colour.
- Most curiously, Targets, people who are central to the Assassin's current objective, whether it's an enemy to be killed, an ally to be protected, or a civilian to be quietly watched, glow a bright shining gold colour, leaving behind a gold trail in the air that makes tracking them easier.
- Eagle vision also outlines things the Assassin can use to avoid detection; groups of people he can blend with, benches he can sit upon to disappear into plain sight, and haystacks he can throw himself into all glow a noticeable white.
In the original Assassin's Creed, Eagle Vision was not actually a real thing; it was described as a function of the Animus, to simulate the extremely highly-trained sense of observation that an Assassin would possess, implying that although an Assassin could determine the intentions of another person at a glance, the bright highlighted colours were not actually part of this ability. This made it all the more confusing at the end of the game when, thanks to the "bleeding effect", in which aspects of the Animus subject's genetic memory become confused with aspects of their own memory, subject Desmond Miles was actually able to use Eagle Vision in the real world, with it later being specifically stated that Desmond had absorbed the ability from Altaïr Ibn-La'Ahad, who had possessed it in life. In Assassin's Creed, the player had to stand perfectly still to use Eagle Vision, at which point the camera cut to a first-person perspective, and it could only be triggered if the player had full "synchronization", though fortunately the first game featured regenerating health.
This explanation was retconned in Assassin's Creed II, which explained that the Assassins really could see the otherworldly colours and highlights, and that it was a genetic quirk derived from a person being descended from Humans who mated with "Those Who Came Before". From this game on, Eagle Vision could be used no matter the player's synchronization level, and it could be toggled on and left on as they moved around, with the camera remaining in third person mode, making it much more useful.
It was also stated in Assassin's Creed II that the player's ability to use Eagle Vision was because of Desmond's ability to use it; the ancestor he was following, Ezio Auditore, did not have the gift, and had made his way through life without it. This last fact was also retconned in the following game, Assassin's Creed: Brotherhood, which stated that Ezio did have Eagle Vision, with the fourth title, Assassin's Creed: Revelations, going as far to say that late in his life, Ezio reached a rare mastery of the ability, a more powerful level called Eagle Sense. Revelations also stated that Desmond now possessed the ability not because he had 'absorbed it' from Altaïr, but because he himself had the genetic code for Eagle Vision, and that the ability had somehow been 'unlocked' by his time synchronizing with Altaïr.
In addition to the above abilities, Eagle Sense gave the user a curious psychic ability to track a target, with patrolling guards and targets leaving behind red and gold trails, respectively, and targets of high importance would even leave behind psychic "echoes", silhouettes of themselves endlessly re-enacting their movements to allow the Assassin to track them effortlessly. However, for some reason, this came at the cost of the ability to highlight things the Assassin could use to avoid detection; haystacks, benches, and groups of people to blend with no longer gave off any light.
Eagle Vision returned (under that name) in the following sequel, Assassin's Creed III, in which the ability was possessed not only by protagonist Connor Kenway, but by his father, Haytham Kenway, even though Haytham was a devoted member of the Templar Order, not the Brotherhood. In this game, it functions very much like Eagle Sense did in Revelations, with the exception that hiding places and other things that can help an Assassin (or Templar!) avoid detection are once again highlighted white.
It also returns in the portable spin-off Assassin's Creed III: Liberation, in which the ability is possessed by protagonist Aveline de Grandpré, who is explicitly described in marketing materials as not being an ancestor of Desmond Miles, as well as in Assassin's Creed IV: Black Flag, where protagonist Edward Kenway (father of Haytham and grandfather of Connor) did possess the ability, but seemed to have a weaker version of it. Edward could use Eagle Vision to light up hostile and friendly characters, important targets, and blendable locations, but the ability would deactivate if he ran any faster than a brisk walk, implying that Edward needed to concentrate to maintain Eagle Vision.