A beholder, sometimes called a sphere of many eyes or eye tyrant is a large aberration normally found in the Underdark. These large, orb-shaped beings have ten eyestalks and one central eye, each containing powerful magic. Powerful and intelligent, beholders are among the greatest threats to the world.
Beholders are immediately identifiable, essentially a floating head with one single, cyclops-like eye surrounded by ten smaller eye stalks. Other than this, the main feature of a beholder’s anatomy is its massive, gaping maw. Because of these features, beholders are occasionally known as "spheres of many eyes" or "eye tyrants," although the latter also refers to a specific type of beholder. 
Because their entire body is covered in eyes, beholders have the capacity to see in all directions at once, making it nearly impossible to ambush them while also giving them an unusually high degree of perceptive ability. Although beholders lack the capacity to see color, they have the ability to perceive even in the most darkened environment, under conditions in which a human or similar creature would be rendered blind.
Beholders are also capable of flight, in spite of their lack of wings or similar physical features, simply hovering above ground effortlessly. The effects of this flight resemble those of the wizard spell levitation. 
Beholders are not particularly strong but are inherently magical creatures, each of their eyes possessing an innately magical nature. Beholders, who often attack for seemingly no reason, will often try to end a battle as quickly as possible, unleashing their terrifying abilities all at once. Among the most basic of these attacks is their deadly ability to project magical power from their eyes, in varying forms such as instilling fear within, charming, knocking out, petrifying, disintegrating, slowing, or killing their enemies.  Any combination of these is possible, although they often use only two at a given time. 
Many, but not all, beholders also have the capacity to use their central eye to project a field of antimagic, which cancels the effects of all supernatural abilities within a small cone of 150 feet in length. In addition to enemy spells, prayers, or similar effects this also affects a beholder's own eye rays, suppressing their power. However, the lack of the ability to cast its eye rays at full strength is hardly a hindrance, as turning to face its enemies in this manner also allows a beholder to attack them with its large, toothy maw.
Beholders are often found occupying deep, underground caverns. Frequently, these lairs are carved out by the beholders themselves, using their eye rays to mold the environment for their purposes. Often, these lairs are built vertically rather than horizontally like most buildings, with beholder architecture frequently exhibiting a large number of vertical shafts which beholders and other flying creatures can use with ease, while walking creatures find their navigation hindered.  Beholders worship Gzemnid and the Great Mother.
Xenophobic yet vicious creatures, beholders are quick to attack enemies, including anyone they deem not "like themselves." Beholders, as a rule, are violent and greedy, hungering for both wealth and power over others. This is made all the more complicated since more than one variety of beholder exists, each believing itself to be the pinnacle of bodily perfection and they view other beholders who differ from this image in even the most minute details as loathsome enemies and inferiors.
Beholder minds are divided into two separate entities. Each of these entities thinks and acts on its own accord even though it is bound to the same body as the other half of its mind. Neither half of the beholder's mind trusts the other, so they hide a lot from each other, creating a very paranoid relationship. "Sane beholders" are beholders whose minds are not "divided" so to speak. There are still two entities within the beholder, but neither hides anything from the other, making a less paranoid beholder. However, the persona of a "Sane beholder" is just as likely to be considered "insane" by anyone else as the persona of any other beholder. Because there are two entities within a single beholder, that beholder should always be recognized by its full name when in conversation with them, or they will perceive it as speaking to only one of the entities.
In spite, or perhaps because of their hatred of diversity, beholders come in a variety of forms, some of which are listed below.
- Bloodkiss beholder
- An undead beholder which sucks its prey dry of blood with its eye tentacles. Also sometimes referred to as a Deathkiss beholder.
- Death tyrant
- Death tyrants are undead beholders akin to zombies.
- Elder orb
- These beholders are born with amazing longevity, to near-immortality.
- Eye of flame
- An unusually docile form of beholder whose members, while still malevolent, are willing to serve beneath more powerful beholders.
- Eye of frost
- A cruel beholder who lives in solitude.
- Ultimate eye tyrant
- An enormously powerful variant of beholder with the capacity to stun nearby enemies as well as a greater range of eye ray abilities.
- Hive mother
- Hive mothers have the ability to magically dominate other beholders.
A vast number of beholderkin exist. Not true beholders, these creatures do not share the race's xenophobia, although most are still quite evil and cruel in nature.
- Death Kiss
- This creature's eyestalks are replaced with blood-draining tentacles.
- Beholder hive shock troopers.
- Eye of the deep
- A aquatic subspecies of beholder. It most notable physical change is it's two large clawed arms.
- An eyeball is a tiny beholderkin with four eye stalks.
- A Gauth is a subspecies of beholders specifically bred to combat spellcasters.
- Ruthless carnivores that hunt beholders.
- An Observer is one of the most socially adept of the beholder family.
- An overseer resembles a large, fleshy tree with mouths on its trunk and eyes on its branches.
- A spectator is an extraplanar beholderkin with four eye stalks.
- ↑ Skip Williams, Jonathan Tweet, Monte Cook (July 2003). Monster Manual 3.5. (Wizards of the Coast), p. 26. ISBN 0-7869-2893-X.
- ↑ 2.0 2.1 Skip Williams, Jonathan Tweet and Monte Cook (October 2000). Monster Manual 3rd edition. (Wizards of the Coast), p. 24. ISBN 0-7869-1552-1.
- ↑ 3.0 3.1 Mike Mearls, Stephen Schubert, James Wyatt (June 2008). Monster Manual 4th edition. (Wizards of the Coast), p. 32. ISBN 978-0-7869-4852-9.
- ↑ 4.0 4.1 4.2 4.3 4.4 Skip Williams, Jonathan Tweet and Monte Cook (October 2000). Monster Manual 3rd edition. (Wizards of the Coast), p. 25. ISBN 0-7869-1552-1.
- ↑ Jeff Grubb and Kate Novak (August 1997). Finder's Bane. (Wizards of the Coast), p. 216. ISBN 0-7869-0658-8.
- ↑ Rich Redman, James Wyatt (May 2001). Defenders of the Faith. (Wizards of the Coast), p. 93. ISBN 0-7869-1840-3.
- ↑ Skip Williams, Jonathan Tweet and Monte Cook (October 2000). Monster Manual 3rd edition. (Wizards of the Coast), pp. 24–25. ISBN 0-7869-1552-1.
- ↑ Bruce R. Cordell, Eytan Bernstein, Brian R. James (January 2009). Open Grave: Secrets of the Undead. (Wizards of the Coast), p. 132. ISBN 0786950692.
- ↑ James Wyatt and Rob Heinsoo (February 2001). Monster Compendium: Monsters of Faerûn. (Wizards of the Coast), p. 24. ISBN 0-7869-1832-2.