Their not completely based off the actual Zodiac signs but more like their based off the Lucavi and Totema from the FFT series. Though four of them are also based off former FF bosses.

Belias The Gigas - Aries: FFTactics Fans will remember him as the Lucavi Wiegraf transformed into. He's XII's Fire Summon. You'll fight him in the story.

Chaos Walker of the Wheel - Taurus: Based off FFI final boss Chaos, He is the Wind Elemental Summon. He's located in the Nabudis ruins and he seals the Attack command when you face him.

Zalera The Death Seraph - Gemini: He's the Lucavi that Elmdore transformed into in FFTactics. His element is Death. He's in the hidden area of the Baraheim Passage and requires you to get a key from the Sick Man in the Desert quest. He must be defeated in five minutes or the battle will reset and you'll have to start over.

Zeromus The Condemner - Cancer: Based off the final boss of FFIV. His elemental is Gravity and his Big Bang attack is one of the strongest attacks in the game. He is located in a hidden part of the Stilshrine of Miriam and he seals the Magick command.

Hashmal Bringer of Order - Leo: He's the Lucavi Folmarv transforms into in FFTactics. He is the Earth Elemental Summon and he's encountered in the story. He is also the only magical earth spell your party gets.

Ultima The High Seraph - Virgo: The Final boss of FFTactics and the Totema for the Nu Muo in FFTAdvance. She is the Holy Elemental summon and her Ultimate attack is a bitch in a half to use. She is located in a hidden section of the Crystal and cycles through all the seals on your parties abilities (no attack, no magic, no items, no techniques, gravity effect, and HP sap) and gains a unique one that saps your MP. She is easily one of the hardest optional boss fights in the game.

Exodus The Judge-Sal - Libra: Named after a different translation of ExDeath's name he was also the Totema for the Viera race in FFTAdvance. His element is said to be Aether in some guides, but its really non-elemental as he uses Meteor as his Ultimate Attack. He's fought in a secret section of the Mosphoran Highway and he seals your item command.

Cuchulainn The Impure - Scorpio: He was the Lucavi Cardinal Delacroix transformed into FFTactics and was the first Lucavi fight. His element is Poison and he is fought in a hidden section of the Garamsythe Waterway under Rabanastre. His battle involves a permanent HP sap on the party.

Shemhazai The Whisperer - Sagittarius: She is unique cause she is neither a final boss from an FF game nor has she appeared as a Lucavi or Totema in previous Ivalice titles. Her element is Soul, but its really Death and she's a bit like XII's version of Odin if you ask me but maybe its the horse thing. She is encountered in the story.

Adrammelech The Wroth - Capricorn: FFTacics fans will remember him as the Lucavi Dycedarg transformed into. He's also the Totema for the Bangaa in FFTactics. His element is Lightning and he's encountered in a section of the Zertinan Caves. He is usually the first optional Esper you can challenge.

Famfrit The Darkneing Cloud - Aquarius: His title gives the impression it may actually be a reference to Cloud of Darkness from FFIII. He first appeared as a Totema from FFTAdvance for the Moogle race. Its element is Waterand it is the only offensive spell that uses higher tier water elemental magic that the party can use. Its is encountered in the story.

Mateus The Corrupt - Pisces: He is named after the Emperor from FFII (Mateus is his name from the Japanese only novels) and first appeared as Totema for the Humes in FFTAdvance. He is a Ice elemental summon and is encountered in the story.

Zodiark Keeper of Precepts - Ophiuchus/Serpentarius: Is the ultimate summon in the game and first appeared in FFTactics as a secret summon used by the games optional boss Elidibus. His element is Darkness but his ultimate attack is non-elemental and does roughly 50,000 damage. He is encountered in a hidden dungeon located in the Henne Mines, that can only be accessed by getting the key in Jahara after you have 10 Espers and have defeated the Mark Catoblepas. Zodiark doesn't pull any weird gimmicks in his fight but his Darkga attacks has an instant death property, and their is no 100% sure way to protect yourself from instant death magic so its not uncommon to see your main party get completely wasted by his first attack. He is easily the cheapest boss in the game.