Most Interesting / Strongest Final Fantasy main antagonist?

What is the strongest and most interesting final boss in a Final Fantasy in your opinion? When explaining who, also explain why.
You can explain based on:
-Difficulty
-Unique abilities and features
-Bio, such as how he became powerful
-etc...

I chose Exdeath because he was pretty difficult, but every boss seems to have it's flaws and glitches. There is a mix you can do with the Alchemist or whatever and instantly kill Exdeath. >_<
Kefka is a really fun boss, but wasn't too difficult. The reason I started hacking FFVI in the first place was because of a video I saw where Locke one-shot him with Genji Glove+Offering and Atma Weapons.

Exdeath for me (NOT BECUASE OF ZEEMIS) ffV is my favourite game and even when I mastered all the jobs and used freelancer he was....easy but still posed a big threat and I like the background for Neo Exdeath and by far my favourite final boss track ( followed by a few like battle scene 2, dancing mad, chaos, this is the last battle and Zeromus ) and he was a tree.....Exdeath for President of Nature! or somthing.

I chose ExDeath because he was by far the strongest of all bosses.Plus FFV was the first Final Fantasy i played.Sephiroth was not that hard and so was Kefka and Zeromus as well as the Dark Cloud and all the others.And this is my 2nd favorite battle theme,the first being clash on the big bridge.

I chose ExDeath because he was by far the strongest of all bosses.Plus FFV was the first Final Fantasy i played.Sephiroth was not that hard and so was Kefka and Zeromus as well as the Dark Cloud and all the others.And this is my 2nd favorite battle theme,the first being clash on the big bridge.

It kinda just goes to show that Square-Enix/soft doesn't really make hard bosses. >_<;

My fav is Ultimecia.
She's badass because of her Hell's Judgement, reduces all your characters' HP to 1. Plus if you don't defeat her down part quick, she will draw Apocalypse which is even more epic and tragic then HJ.
I also love her backstory. A sorceress from the future which wants to compress time, and probs because she's Rinoa and wants to see Squall back. If you are against the whole Rinoa is Ulty, well, too bad. I am not.

(Off topic, i'd like Eden to be a real Garden in FF8.)

my toughest final boss was zeromus. kefka was a close 2nd and to the voting poll necron should've been added since there are hints and explanations to his appearance in the game.

Easily "the Great Jecht." For one he has a tendency to drink heavily. In fact once he was drunk and mistook a Shoopuf for a Fiend and attacked it, forcing Braska to pay for the damage with all of his travel money. XD I can relate with that. And he disliked Tidus almost as much as I did it seemed. Despite his numerous flaws, at heart Jecht is a good man, and...SPOILERS!!!

...gave up his life to become Braska's Final Aeon. He enjoys the Hymn of the Fayth, as do I.

i think the cloud of darkness/dark cloud was the hardest boss basically because of its particle beam and on top of that if you dindt kill 4 other bosses then particle beam did 9999 damage i dont know about flare wave though cause i never got to the end of the nes ff3 also i found kefka the easiest boss

I chose Artemecia. (thats what the name Ultimecia was based on)
Because even when capped, she can still pwn your ass. How? well
if your not spamming lionheart or not having that kind of sword nor those heros/ holy wars/ invincable buffs..

She can be a b*t*h, she can still own ya if your not careful.

Kefka was easy, so was sephiroth, so was Kuja, I only faught Kuja a couple times and he was easy, even for my first try. XD
Dunno why he has high rating, same for kefka. Sounds like popularity, but meh. XD