Ifrit

Ifrit is a fire-elemental summon which appears in several games in the series. His attack is called Hell Fire (sometimes called Inferno or Flames of Hell), and deals fire-elemental damage to all opponents.

Final Fantasy IV
Ifrit is automatically obtained when Rydia joins for the second time. He is called Jinn in the Super Nintendo release.

Final Fantasy V
Ifrit is a Level 2 summon found in the Ancient Library, where he must be fought to be obtained. There is dialogue between him and Shiva if the player managed to find her.

Final Fantasy VI
Ifrit is an Esper whose magic power was completely drained. Along with Shiva, he was discarded by Kefka Palazzo in the Magitek Research Facility. He is obtained by being defeated along with Shiva in the garbage chute, where he realizes that party posesses Ramuh's power, and he offers himself up as Magicite. His attack's Spell Power is 51, and it is unblockable. He costs 26 MP to summon. He teaches the following spells:
 * Fire X10
 * Fire 2 X5
 * Drain X1
 * At Level Up: Vigor +1

Final Fantasy VII
The Ifrit Materia can be found on the Shinra boat after defeating Jenova BIRTH. Its attack is called "Hellfire", costs 34 mp to cast and causes fire based damage to the entire enemy party.

Level -- AP Needed
 * Level 1  --    0
 * Level 2    --  5000
 * Level 3   --   20000
 * Level 4    --  35000
 * MASTER   --   60000

Stat Changes
 * Magic +1
 * Maximum HP -2%
 * Maximum MP +2%

Final Fantasy VIII
Ifrit is the third Guardian Force available. He is obtained by defeating him in the Fire Cavern before the time limit runs out. He is also somewhat unique in that he talks during the battle, and expresses surprise and alarm if you summon the Guardian Force Shiva during the battle.

Final Fantasy IX
Ifrit is obtained automatically from Doctor Tot at the beginning of Disc 3. It is learned through the Topaz, and only Princess Garnet can summon it.

Final Fantasy X
Ifrit is an aeon that is found in the Kilika Temple. Its unique ability is called "Meteor Strike", in which he conjures a ball of firey rock and punches it towards the enemy, which penetrates the "Protect" spell. Wakka's World Champion weapon allows it to break the damage limit.

Final Fantasy X-2
Ifrit is an aeon that is possessed by Shuyin to help him take over the world due to his lost love, quite similar to Yuna, Lenne.

Final Fantasy XI
Ifrit appears as one of the 6 prime avatars in Final Fantasy XI. Avatars are available only to Summoners or (less sensibly) a character with a subjob of Summoner in XI. Ifrit is not as often used for casting party-benefiting spells as many of the other Summons included in Final Fantasy XI. Instead, his strength seems to be doing larger amounts of raw physical damage.

Final Fantasy Tactics
Ifrit appears as a bull and performs a fire attack when summoned.

Final Fantasy Tactics Advance
Ifrit appears as a warrior clad in red armor with bull horns on his helm and large gauntlets and deals fire damage when summoned.

Etymology
In Arabian mythology, Ifrit (also spelled Efreet or Afreet), is the name given to a class of Jinn (magical spirits also known as Djinn, Djinni and Genie) that embody fire. Though they could live for thousands of years, they were not immortal, and if cut, they would "bleed" the fire running through their veins, until it consumed their bodies. Jinn tend to be arrogant creatures whose power can occasionally be harnessed by humans, much to the Jinn's chagrin (which is implied when challenging and defeating Ifrit in Final Fantasy VIII). In the Super NES release of Final Fantasy IV, Ifrit was called Jinn.