An Conjurer is a form of Specialist Wizard in Dungeons & Dragons. As their name suggests, these wizards focus their attention on the magic school of Conjuration, the art of calling forth beings from other planes to serve their bidding. These are minion-master wizards, and one of the styles traditionally most hated by DMs and other players alike; not only can their personal army of summoned goons make combat go on for ages (since said summoner has to not only add several new turns to the round, but also look through long lists of monsters to get what they want and keep track of their stats), but their ability to command the magical powers of the creatures they summon makes them hugely overpowered. A classic example is the Conjurer summoning a creature that can then summon other creatures, leading to an exponential increase in minions - and this is one of the lesser ways they can abuse its potential. (Note that most modern editions make it clear that summoned monsters lose their own summoning powers.)
However, this school also deals with dimensional and planar travel, meaning all manner of potent and useful spells like teleport, plane shift, and even the humble dimension door are also covered by this specialization. It's just that the creature-summoning angle gets all the press. In fact, this even led to the abortive attempt in Advanced Dungeons & Dragons to create a separate kind of specialist wizard, the Dimensionalist, to represent a wizard focused on dimension-manipulating magic.
In a way, the conjurer of Advanced Dungeons & Dragons was a precursor to the CoDzilla of 3e. Summoned monsters, even at low levels, made the fighter feel superfluous, and then when the conjurer grew strong enough to call up creatures that could cast their own buffs, they could essentially run the game all by themselves.
The conjurer archetype is so strong that Pathfinder actually created an entirely new class, the Summoner, to be a more "balanced" version of the conjurer by cutting away pretty much all of the wizard spells that weren't conjuration spells. However, some still consider it busted, if only because it can cast summoning spells as a standard action instead of a full-round action, plus it gets a pet to twink out with custom traits. It is the only class to be so-completely reworked by its Unchained variant that most pretty-unanimously consider it a nerf, and unlike the other Unchained classes, playing its old form in official games is no longer allowed.
Ironically, Conjurers are the only specialists other than Necromancers who seem to get generally perceived as evil, mostly because of the cultural archetype has them summoning fiends from the Lower Planes. In fact, Advanced Dungeons & Dragons 2nd edition had a Necromancer kit called the "Undead Master" who strove to be an archetypical "pulp style" Evil Wizard by basically being a triple-classed Conjurer/Enchanter/Necromancer. Even without the fiend-summoning, though, there is something a bit dodgy about calling up other creatures and enslaving them to your will to fight your battles for you, as opposed to the "honest" wizarding method of just blasting the shit out of enemies with magical might.
4e's Drastic Changes
When Dungeons & Dragons 4th Edition did its drastic reinventions of classes to put an end to the problem of Linear Warriors, Quadratic Wizards, naturally, the Conjurer was near the top of their list of potential problems to iron out. Their solution was to break the old Conjuration school into two keywords; Conjuration and Summoning.
Conjuration is summoning of the Final Fantasy style; it summons a creature (or an elemental effect) as part of an attack; the conjured critter lasts for a short while, typically either until the end of your next turn or so long as you sustain it with a minor action, and then fades away. Whilst it lasts, it typically creates a passive effect, and sometimes uses other user actions to repeat its initial attack. The conjuration has no hit points and no statistics; it does what it does, and is then gone.
Summoning, on the other hand, is closer to old school D&D conjuration; it summons a creature that fights for you as an extra player on the battlefield. Summoned creatures have defenses equal to the summoner's, hit points equal to their bloodied value, drain a Healing Surge with them if killed (or HP equivalent to half the summoner's bloodied value, if they have no surges left), have no innate healing surges (but can spend their summoners), and use the summoner's action points for their own. This prevents summons from increasing the amount of time that a summoner needs to do things on their turn, and discourages the "use summons as meat shields" angle of old, so a summoner in no way renders the fighter obsolete. Most Summoning spells are Attacks, but some are Utilities.
It took WotC a while to come up with this idea. Originally, only the Conjuration keyword existed, and all Conjuration spells from the Player's Handbook were daily. It wasn't until the Arcane Power splatbook that wizards were furnished with both Encounter Conjurations and Summons. However, all Summons are daily powers, which further prevents the "flood the battlefield with expendable bodies" tactic that so aggravated DMs in editions past.
By 4th edition's end, only one other class using the AEDU System had access to Summons; the Druid, who gained them (plus a Summoner Druid "archetype") in Primal Power. Druidic summons came with a new trait; Instinctive Effects. These gave each Summon a specific behavior that it would undertake if the player didn't assign any specific actions to their Summon on their turn. This made them less of an action drain whilst still not drastically lengthening the player's turn.
Inspired by this, an article in issue #385 of Dragon Magazine, "Class Acts: Wizard" would further bolster the wizard's list of summoning spells, and create a new pair of mechanics. Intrinsic Nature is, functionally, identical to Instinctive Effects - except that whilst some druidic summons will make the distinction between the druid and her allies and others will just blindly attack any creature, including their summoner or allies, all wizard summons with the Intrinsic Nature trait will just go after whoever is closest, friend or foe. Plus, there will be some kind of magical backlash against the caster for leaving them uncontrolled. The second mechanic is Symbiosis; a permanent passive bonus that the wizard gains so long as their summoned creature is present.
List of 4e Summoning Spells
- Arcane Power
- Level 1: Summon Fire Warrior
- Level 2: Summon Shadow Serent
- Level 5: Summon Abyssal Maw
- Level 6: Summon Iron Cohort
- Level 9: Summon Arrowhawk
- Level 10: Summon Hammerfist Crusher
- Level 15: Summon Chainbearer
- Level 16: Summon Diamond Falcon
- Level 19: Summon Black Devourer
- Level 25: Summon Abyssal Horde
- Level 29: Summon Living Mountain
- Dragon #385
- Level 1: Summon Dretch, Summon Dust Devil
- Level 5: Summon Imp, Summon Magma Beast
- Level 9: Summon Hell Hound, Summon Succubus
- Level 15: Summon Stormstone Fury, Summon Vrock
- Level 19: Summon Couatl, Summon Rockfire Dreadnought
- Level 25: Summon Earthwind Ravager, Summon Marilith
- Level 29: Summon Balor, Summon Djinn Stormcaller
5th Edition's Arcane Tradition
Conjurers, as you might expect, focus on buffing up their conjuring skills. Minor Conjuration (level 2) lets them immediately conjure up any small item they need whenever they want. Benign Transposition (level 6) lets the conjurer teleport 30 feet or tele-trade places with a creature of their choice within that distance; this can normally only be done once per day, but a Conjuration spell lets them refresh that timer automatically. Focused Conjuration (level 10) means they no longer need to take concentration checks as a result of taking damage, so long as they're concentrating on a Conjuration spell. Finally, the humble Durable Summons feature (level 14) grants +30 temporary hitpoints to all summoned and conjured creatures.
However, thanks to the tweaks made to the core system via the concentration mechanic, the paucity of spells that actually summon monsters of worthy power for the spell slots they consume, and a number of other subtle system tweaks in the edition, it's still fairly weak, just because summoning, possibly because of the reasons above, is almost-deliberately fairly weak now.