Esper (Final Fantasy XII)

There are thirteen Espers which the player can obtain (those in italics are not encountered in the course of the game's storyline):

Level One Espers (require one Mist Charge to summon)
Belias, the Gigas (The Tomb of Raithwall)

Mateus, the Corrupt (The Stillshrine of Miriam)

Adrammelech, the Wroth (Zertinan Caverns)

Zalera, the Death Seraph (The Barheim Passage)

Level Two Espers (require two Mist Charges to summon)
Shemhazai, the Whisperer (Giruvegan)

Hashmal, the Bringer of Order (The Pharos)

Cuchulain, the Impure (The Garamsythe Waterway)

Zeromus, the Condemner (The Stillshrine of Miriam)

Exodus, the Judge-Sal (The Mosphoran Highwaste)

Level Three Espers (require three Mist Charges to summon)
Famfrit, the Gathering Storm (The Pharos)

Chaos, the Walker of the Wheel (The Necrohol of Nabudis)

Ultima, the High Seraph (Giruvegan)

Zodiark, the Keeper of Precepts (The Henne Mines)