Invoker

Invoker is an almighty ranged intelligence Hero, considered by many as the most complex and difficult to use. He is unique in that he possesses a total of 14 abilities in his arsenal; three of them - Quas, Wex, and Exort - are reagents and one is his special ultimate Invoke. The three abilities he learns throughout leveling up can have three instances, which serves as the basic ingredients or components for him to create a new ability using his ultimate. Once the reagents or elements are combined, he can invoke one out of ten different abilities. All of his invoked abilities are capable of a multitude of actions, from damaging enemies to aiding his allies, and even saving himself from danger. His three reagents can be upgraded up to level 7 which determines the power and potency of his invoked abilities, making it more powerful than an ordinary spell. Because of this, he can be played in almost any role possible. Invoker can be a carry, semi-carry, ganker, pusher, initiator or even tank or support (though the gold investments on both make this highly unrecommended). He is also the only hero who doesn't have Attribute Bonuses, thus he has average attributes. However, his three reagents provide passive attributes with each level, and each instance of his reagents provides a passive bonus, allowing for specialization at early levels and situational boosts at later levels.

The Invoker, though powerful on his own, is item-dependent; his top priorities are health for his survivability, mana for him to utilize more of his abilities, and damage if you want him to be a strong carry. The result is his differentiating item build in almost every different situation, mostly depending both on his own build, and his opponents' actions. He also requires fast hands, and various skills depending on the focus of his invoked abilities; examples include his need of extreme map awareness to pull off Sun Strike properly, or to have a subtle idea of prediction to pull off combos such as EMP - Tornado or vice versa. Because of this, newer players will have a hard time using Invoker. But once learned and mastered, the Invoker will rise to its full potential and playing this archmage is truly a great reward. Invoker is recommended for advanced players.

Gameplay
The Invoker is the most well-rounded spellcasting hero, due to his massive array of spells. Using his three elemental reagents and his Invoke ability, the Invoker can utilize a total of 10 different spells. Due to his complexity and fragility, the Invoker is a bad choice for newer players. With some experience, however, he becomes a force to be reckoned with. The Invoker is capable of massive area of effect damage, powerful disabling spells, very strong summons, and potent enchantments. While other spellcasters tend to be focused in one area, the Invoker has the ability to change his role at will. His spells tend to start out weaker than comparable abilities, but since his reagents have 7 levels each his potential spell power is very high. Although mastering his spells takes perhaps the most practice of any hero, he is definitely worth the time.

At level 25, Invoker has 7 points each towards Quas, Wex, and Exort, and 4 points towards Invoke. Uniquely among heroes, Invoker does not possess the Attribute Bonus ability (i.e., he cannot put points towards "Stats"). Instead, he gains a permanent attribute bonus to one of his stats each time he levels up Quas, Wex, or Exort.

Due to the removal of mana cost and drastic reduction in cooldown of Invoke, Aghanim's Scepter is a crucial item in almost any of Invoker's item builds.

Name
In DotA, Invoker's name is Kael, possibly based on the WarCraft Blood Elf Mage character, Kael'thas Sunstrider. His fun name is Kal-El, a pun conflating the name Kael with the birth name of Superman.

In April 2011, a leaked DotA 6.72 Chinese changelog referred to Invoker as "卡尔" ("Kael"). A PlayDota forum member translated the changelog with Google Translate, in an attempt to get a quick, rough translation. Google Translate mistakenly translated "卡尔" as "Carl". Google Translate botched a number of other hero names, including "Just back beast", "Giant Sea Man Tooth", and "Crypt compilers". PlayDota forum members were at first confused, then entertained by the mistake. IceFrog, the lead developer of DotA and Dota 2, and who speaks Chinese, joked "Carl had it coming".

In December 2011, drafts of Invoker's Dota 2 lore referred to him as "Garral" twice, presumably a nod to "Carl". This name was excised upon Invoker's release in January 2012; the lore currently refers to him only as "the Invoker".

Invoker's voice lines include the name Carl three times. Invoker has a small chance to speak one of these lines when his model is selected: The latter lines are intended to be humorous. One equates the awe-inspiring "name of power" with the mundane "Carl"; the other sillily spells the name in all-capital letters.
 * invo_spawn_01.mp3 "Carl!"
 * invo_rare_04.mp3 "Throughout the aeons I have been known by many names…but my true name of power…is Carl."
 * invo_rare_05.mp3 "Behold before you, the illustrious, the imperious, ingenious arch-mage… CARL."

Undying uses the name Carl once, when meeting an allied Invoker on the battlefield, and even then only 5% of the time: However, Undying also uses fourth-wall-breaking jokes to refer to other heroes, such as: Undying also refers to himself as "Bob", despite being "Undying, the Almighty Dirge" elsewhere:
 * undying_ally_10.mp3 "Carl, is that you?"
 * Bounty Hunter, Spirit Breaker, Venomancer, Alchemist: "Hunter", "Charger", "Spitter", "Jockey". References to Left 4 Dead, with only a 25% chance of playing.
 * Tinker: "For Lamarr." A reference to Half-Life 2. (Currently unused.)
 * "No dead are safe from Blueheart Bob." (Currently unused.)

Mirana uses the name Carl once, when killing an enemy Invoker, and even then only 5% of the time:
 * mir_rival_16.mp3 "Carl, meet Sagan." A pun on Carl Sagan. (Mirana's feline mount is named Sagan.)

In summary, whether Invoker's "real" name is Carl appears to be a subject of humor and intentionally ambiguous.

Trivia

 * In the earliest version of Invoker, the order of instances mattered when Invoke was cast. Invoker had access to 27 spells, including the 10 still in game.
 * Invoker is (or used to be) a Magus like Rubick, who calls him the Arsenal Magus.