Notes

Abaddon
Abaddon's title, Lord of Avernus, is a reference to the famous crater in Italy, which was, in ancient times, believed to be the entrance to the underworld.
In the Hebrew Bible, "Abaddon" means bottomless pit, usually appearing in reference to "sheol," meaning the realm of the dead, or a grave.
In the Christian Bible (Book of Revelation, to be specific), Abaddon is described as a "destroyer", the angel of the abyss, who will rise from the Abyss and command a plague of locusts resembling horses with crowned human faces, women's hair, lions' teeth, wings, iron breast-plates, and a tail with a scorpion's stinger that torments for five months anyone who does not have the seal of God on their foreheads. Some older beliefs state that Abaddon is the Antichrist, or even Satan (who we'll talk about later). The Methodist publication "The Interpreter's Bible" states: "Abaddon, however, is an angel not of Satan but of God, performing his work of destruction at God's bidding."

Alchemist
At one point of the beta, Alchemist's lore was simply "Alchemist is named Al and is a chemist."
One of Alchemist's last hit lines "Only 98% pure?" is a reference to the popular AMC TV series, Breaking Bad
Alchemit's line "Better Living Through Alchemy!" is a reference to the phrase "Better Living Through Chemistry", a popular variant of a DuPont advertising slogan which later became a common phrase.

AA
Ancient Apparition's name, "Kaldr," is old norse and translates to "cold"
His lore suggests that he is the embodiment of the Heat Death, a theoretical fate of the universe. According to this theory, the universe will achieve thermodynamic equilibrium and will no longer transfer energy. This would result in a universal temperature growing colder and an end of processes that require energy consumption, such as life.

AM
Anti-Mage's DotA 1 name was Magina, and taken out of Dota 2 for no known reason
In DotA 1, Terrorblade and Anti-Mage were twin brothers, but this was not brought over to Dota 2. However, there are many unused lines when killing or meeting Terrorblade referring to them as brothers, such as "Hello, brother"
According to his Dota 2 lore, Anti-Mage is the lone survivor of the Turstarkuri monks, who were taken out by the Legion of the Dead God, an army of undead soldiers whose purpose was to spread the Dead God worship. The legion supreme commander is none other than Undying. "To thy Dead God go."

Arc Warden
In DotA 1, Arc Warden was a Gnoll, a canine-like creature from Warcraft. Lines such as "Hounding," "Doggedly," and rivalry lines towards Lycan such as "Inferior Form," are references to this.
The line "You will just have to accept this and move on" is a reference to the Youtube cartoon "the Dota 2 reporter" as a running gag where characters would question the game's logic only to be answered by this.
As mentioned in Dota 2 lore, Zet was a supposed "third" ancient, alongside Dire and Radiant. Many of his voice lines, especially victory or defeat ones shows that Zet is almost the neutral team in the world of Dota. He guards both ancients, according to lore.

Axe
Axe, Disruptor, Warlock, and possibly Lifestealer are all related, coming from the Oglodi tribe.
Axe's name (Mogul Khan), his lore, and "one man army" image is a reference to Khan from Star Trek, who was also described as a one man army.
His line "Better red than dead" is a reference to the Cold War slogan "better dead than red," red being a symbol of communism. So in other words, Axe is a die hard communist.

Bane
Bane's name, Atropos comes from Greek mythology. One of the Moirai Sisters (commonly referred to as the Sisters of Fate), Atropos was the sister in charge of cutting the "Life Thread" of those who were going to die. Her name literally means 'The No-Turning One,' referring to the irreversible and inevitable destiny of death.
Bane's line "Sleep no More" is a reference to Shakespeare's "Hamlet," in particular, his "to be or not to be" soliloquy. Hamlet reasons over whether to take his own life or carry on with the lines "To die, to sleep-. No more-and by a sleep we say to end..."

Bat
Batrider's DotA 1 name was "Jin'Zakk," which in my opinion is an awesome name that should have never been taken out of Dota 2
Batrider rides what is known as a "Morde-Bat," which is apparently a fruit bat according to the line "it ain't the bat ya gotta worry about, she eats fruit." Which begs the question, what does Batrider himself eat?
Batrider is from the Yama Raskav Jungle. Medusa's Bow of the Serpent is crafted from the wood of the grove where a unique singularly deadly species of viper lives. And not the hero Viper. Along with Batrider and Medusa's bow, Almond the Frondillo comes from the Yama Raskav Jungle. According to Almond's lore, she was "Taken from her home as a pup, escaped her owner, and found her way to an even greater conflict," being Radiant vs. Dire... and Zet?

Beastmaster
Beastmaster's original DotA 1 name was "Rexxar," a character from the Warcraft Universe. His name was changed for copyright reasons. Rexxar was the main character of the bonus campaign in Warcraft III, and also playable in Hearthstone as "Hunter." In addition, (in WC III, but not Hearthstone) Rexxar wields two axes.
In Dota 2 lore, Beastmaster and Lycan both originate The Kingdom of Slom, and both had to deal with its' unjust ruler, The Last King, in their early childhoods. They do not seem to know about each other's deeds, however, since neither of them talk about each other at all. Kind of explains their thing with animals and uh.. demons? (Necronomicon)

Bloodseeker
Although Bloodseeker has an Aztec or Incan look to him, his name "Strygwyr" is likely a Welsh-influenced rendering of the Romanian word "strigoi," meaning poltergeist, often used in folklore in reference to vampires.
Bloodseeker is from the peaks of Xhacatocatl, which are ruled over by the "Flayed Twins." The empire of Xhacatocatl is under the influence of the Flayed Twins, and is bound to supply them with blood lest they suffer the same fate their sole hunter (Bloodseeker) bestows upon others. On this topic, bloodseeker could likely have been a human before having been heavily mutated by the Twins to suit his purpose better.
A symbol of the Flayed Twins is the Raven.

Bounty Hunter
Gondar the Bounty Hunter sometimes talks in a second (perhaps his first) language. The language he speaks is unknown, for there is no translation as to what he says. A couple of these lines are "Fi'ir," "Itam 'gro," "Ahgo 'prira"
In his lore, Soruq the Hunter was a legendary bounty hunter, who may have taught Gondar his special skills before Gondar killed Soruq.
When using track, a small projectile that looks like Alchemist's Unstable Concoction is thrown at the enemy, presumably so that Bounty Hunter can augment his already elevated senses of sight and smell.

Brewmaster
In Warcraft, Brewmasters were Pandaren, as were Brewmaster, Storm, Earth, and Ember Spirit in DotA 1. Though Brewmaster still looks like a Pandaren, he isn't referred as so.
Brewmaster is one of the celestials, alongside aforementioned Storm, Earth, and Ember Spirit. Brewmaster was a special Celesital though, since his primal split uses Wind, Earth, and Fire. Sound familiar?

Bristleback
Bristleback's hero model in DotA 1 was of a quillboar, looking much more like a boar. His name is also the same as a tribe of quillboars in the Warcraft Universe. In beta, Bristleback's name was going to be "Bristlebog," probably to avoid conflict with the aforementioned Bristleback tribe in World of Warcraft.

Broodmother
DotA 1, Broodmother's spiderlings originated from her relationship with Anub'arak, the Nerubian Assassin, now known as Nyx. In Dota 2, such tie between the two heroes does not exist... Thankfully. Think about these two having kids. Now stop thinking about it.
Broodmother's line "Some Pig" is a reference to the classic novel, "Charlotte's Web."
You're still thinking about it, aren't you?

Centaur
Bradwarden is the name of a centaur in the first DemonWars Saga trilogy by R.A. Salvatore
Centaur's DotA 1 title was "Centaur Warchief"
Centaurs of Dota 2 come from the land of Druud, which you may hear from Disruptor's lines plenty and plenty of times. The reason for this is that Druud is the homeland of the Oglodi, and makes a nice place for centaurs to roam free.

CK
In Dota 2, there are the 4 elementals, Chaos Knight being the one of Chaos. The four elementals are Keeper of the Light, Enigma, Wis- pardon me... Io, and of course Chaos Knight.
Chaos Knight loves and is attached to his faithful horse, Armageddon. "Ride on Armageddon" is really kind of a sad line.
Chaos Strike's icon resembles a D20 dice, used in many tabletop RPGs, such as Dungeons and Dragons.
He started his career after what is known as the "great schism," also known as "the big bang," meaning he has existed as long as the universe has, causing chaos (which IS needed in the universe) wherever he goes.

Chen
Chen hails from the Knights of the Fold, which is the sworn enemy of the order of Aeol Drias, where Nortrom the Silencer hails from, making them enemies.
Chen was born in the Hazhadal Barrens, a desert home to godless tribes and the desert Locuchi, an animal that Chen now rides. According to lore, Obelis, the god worshipped by the Knights of the Fold, took in Chen, and now Chen devotes his life to converting people (and animals) to the Knights of the Fold to worship their god, Obelis. Chen is the missionary of Dota 2.
His line "My leg" is a quote from Spongebob

Clinkz
Clinkz hails from the Hoven, which lies at the base of the Bleeding Hills, birthplace of Shadow Shaman.
The line, "Better to run than curse the road." is a reference to a Wolof proverb, "Better to walk than curse the road."
His alternate name is "Brooklyn Kurtz," after a bad translation from Chinese, and has been made into a shirt.
Clinkz was once some sort of a human-like animal, somewhat identical to Riki, before being cursed to never die as his flesh was burned, turning him into the beautiful looking nightmare we all know and love, and OH GOD IS THAT AN 8 MINUTE DESO?

Clockwerk


CM
Dark Seer
Dazzle
DP
Disruptor
Doom
Dragon Knight
Drow
Earth Spirit
Earthshaker
Elder Titan
Ember Spirit
Enchantress
Enigma
Faceless Void
Gyrocopter
Huskar
Invoker
Io
Jakiro
Jugg
KOTL
Kunkka
Legion
Leshrac
Lich
Lifestealer
Lina
Lion
Lone Druid
Luna
Lycan
Magnus
Medusa
Meepo
Mirana
Morphling
Naga
NP
Necro
NS
Nyx
OD
Ogre Magi
Omni
Oracle
PA
PL
Phoenix
Puck
Pudge
Pugna
QoP
Razor
Riki
Rubick
SK
SD
SF
SS
Silencer
Skywrath
Slardar
Slark
Sniper
Spectre
Spirit Breaker
Storm Spirit
Sven
Techies
TA
Terrorblade
Tidehunter
Timber
Tinker
Tiny
Treant
Troll
Tusk
Undying
Ursa
Venge
Venomancer
Viper
Visage
Warlock
Weaver
Windranger
WW
WD
WK
Zeus