Conjurer

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.

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.