Chaos

Chaos is a mysterious concept in the lore of Dota 2, often spoken about by entities of cosmic consequence or other lesser beings who may have an affinity for it.

Description
The definition of chaos is vague because of the sparse information that mentions it, but it is known that chaos is the antithesis of order which is said to make up all of creation. Chaos exists between the stars (likely referring to chaos' original meaning in Greek which is void or vast chasm) and within each scene of battle and strife. Chaos can be made from order and vice versa. Chaos encompasses the following stuff compared to its counterparts in order. Note that some of them may not have a counterpart.

Notable Entities
It's interesting to note that just because the following entities are aligned with chaos, it doesn't mean that they don't have some form of order to their existence. That's the essence of duality, after all.

Heroes
is the paragon of chaos, a physical manifestation of chaos itself. He embodies everything about chaos—randomness, disunity, corruption, darkness,  and other chaotic stuff that he may have intrinsically. Despite all this stuff about chaos, he seems to be compelled to reunite his Fundamental brothers back to their home realm, an act that inclines to order itself. 's powers over light and dark are said to be a blend of chakra and chaos magic respectively.
 * He is capable of bringing others into lower states of order, especially when killing them.

is said to be no different from the Chaos Knight, who even claims that the former is an agent of chaos. Demons in general are said to be chaotic creatures, as stated by one particular demonologist. It's interesting to note that even as an agent of chaos, Doom still abides to the Umbral Pact and is concerned when its ancient equilibrium is about to be destabilized, hinting at his inclination to order.

is an entity devoted to chaos. Although his existence is proof that he is maintained by the stuff of order such as unity and wholeness, not to mention that parts of his master plan have some form of order in them such as wholeness and unity,  there is no denying the chaos in his actions. He seeks to topple the natural order of today's world  so that he can achieve his goal to make a desolate world of chaos. 's very existence is chaotic. Although he claims to be an agent of chaos, he truly embodies it with each of his signature abilities of deception and trickery. He has gained his true immortality after he disrupted his place in the natural cycle of life and death by removing his name from the Book of the Dead, something that the forces of order did not take kindly to.
 * Not only that, but the Impurities that he embodies and is devoted to are corrupt and impure elements, embodying chaos in the form of being corrupt. As its sole agent,  he is the impurifier who wields the power to debase and corrupt nature, so that it may mirror its horrifying core.

is said to have emerged from chaos and causality, likely referring to his home reality that he split into a paradox. His ability to create paradoxes and disrupt the paths of fate and destiny with his abilities makes him an entity of chaos.

embodies the stuff of chaos, especially outside of her natural and eternal form. Hailing from a plane of existence that is full of chaotic, violent energy she is an entity of chaos who is irresistibly drawn towards scenes of conflict in the material plane. When she manifests on a battlefield in the material plane, her otherwise whole form will enter a state of disunity where her identity gets shattered and she becomes multiple entities known as Haunts—fragments of her once whole self.
 * The first line of her bio compares her incarnation on the material plane to entropy, which is (without saying any physics jargon) chaotic with its randomness and uncertainty.
 * One of her Haunts, who has gained individuality after it was separated from the main Spectre by cursed armor, enters a state of dissonance when she dissipates. Her reincarnation undoes this state.

Other Entities
The Radiant and the Dire Ancients, Radinthul and Diruutlh, possess dissonant energies that can warp others into beings of disunity. This dissonance may explain why Zet's own attempts to fuse them both and restore them back to the whole Primordial Mind that it once was before it was broken failed.

Races
According to a certain practitioner of demonology, demons are said to be creatures of chaos. Said demonologist also uses the word "chaos" as a metaphor to describe these dark entities. Besides that, demons usually have the stuff of chaos like corruption, darkness,  deception, destruction,  etc.

Items
The is an arcanist's orb that contains an ingot of chaos suspended in wizard's ether. It's possible that the Obliterating Orb in the card game Artifact is the same item as this orb. The is a horrifying dagger that was forged in the chaos maw. It is virtually untouchable to mortals.
 * In the card art of this orb in Artifact, it is seen in front of a mural that depicts it being used. The mural shows a pair of Radiant and Dire towers being destroyed by the power of this orb. It's also described as an orb that "undermines the most well laid of plans" when used in the right hands. Not to mention that its passive ability is called Impeding Corruption which reduces the target's armor and slows them. As an item of chaos, it has destruction and corruption which are elements of chaos.

DOTA: Dragon's Blood
In this continuity "chaos" essentially correlates to the weak nuclear interaction.