Cid

Cid is the master of the Al-Bhed tribe,
as well as Rikku's father and Yuna's Uncle.
Cid is a NPC (Non Playable Character).

Chocobo's

Chocobo's are the big birds also seen in the other games
in the FF-series. They're used as transportation. Train them in races.
By winning these races, you can earn prizes. If you break your own record,
another prize will be given to you. Prizes will be awarded each
time you break the record.

Aeons

Aeons are powerful creatures that can be summoned.
Summoners go on a pilgrimage, in order to summon the Final Aeon with
which they'll try to defeat Sin. When Aeons are called upon in FFX, all
characters but the summoner leave the battle. Until their HP goes
to 0, or they are retracted by the player, the aeon is playable.
There are 8 Aeons: Valefor, Ifrit, Ixion, Shiva,
Anima, Yojimbo, Bahamut and the Magus Sisters.

Fiends

There are a lot of monsters, fiends,
in the game which you'll have to beat. Some are more
powerfull than others. There are a lot of different types of fiends,
and you'll have to figure out which attack is more effective
to destroy the different types.

Jecht
Tidus' father. He's very rude and keep bothering Tidus. He gives Tidus a sword and Tidus was shocked of his father's action because he has never done it before.

Chappu
Wakka's brother. He was a member of the Suppression Corps, but last year, they attacked Sin and he died in the battle.

Lord Braska
Yuna's father, a summoner. He has defeated Sin and become famous throught out the world of Spira. Yuna becomes a summoner as a tradition.

Great Summoner Orhaland
A summoner who lives in Keelica Temple. He used to be a great Blitzball player but else not known much.

Sin
Sin is not actually a real person, he is more of a evil force. It is said that the last time Sin arose was about 1000 years ago, which sent Spira into its current state. Now he is going to return, for what? We don't know but we know for sure that it is not going to be a good sign, so it is your main job to stop Sin from what he is going to do.