Most overpowered characters in gaming...

[Hollycat]

Count Orlandou Cidolfus is perhaps the most over powered character ever. Excluding the secret enemy from BBS

[Carl the Llama]

[Wolf Kanno]

TBH I am surprised that no one has mentioned any of the FFVII characters, if a level 7 Tifa can beat Emerald weapon with the right materia combo I would say that it pretty damned overpowered, and if Tifa can do it, then so can everyone else.

2) No major exploitation of the battle system, i.e. with VIII's Junction system, any character can solo the game so it has more to do with the system than what is inherent in the character itself.

[BG-57]

Most of the ones I thought of have have been mentioned already (like T.G. Cid and the Suikoden characters) but I have a few contributions:

Suikoden Tactics: Lazlo and Snowe are bonus carryover characters from SuIV. Snowe is an unremarkable warrior type but Lazlo can singlehandedly clear entire battlefieds with his Rune of Punishment.

Arc the Lac II: Choko can do a subquest and unlock Akura, who can wipe the walls with foes.

Arc the Lad III: Anrietta is one of Alec's frequent clients and seems a typical spoiled rich girl, but in combat she can deadly fire energy beams! She's below the main characters' levels if recruited, but once she's brought up to speed she's more powerful than anyone else.

[Del Murder]

Canopus from Tactics Ogre. Or Arycelle. Or any archer. But Canopus first because he can fly.

[Roogle]

BOF II was pretty overpowered with Blue. She is everything Nina is, but better.

Yes, Bleu completely overrides Nina as a character in the gameplay mechanics. She has the highest growth in almost every parameter because her statistical growth increases even at levels where other characters' stop gaining points in various statistics.

Rose was fairly powerful in Street Fighter Alpha 2. If I recall correctly, Rose, Chun-Li, Ryu, and Ken make up the top tier by themselves.

[Polnareff]

Rose was fairly powerful in Street Fighter Alpha 2. If I recall correctly, Rose, Chun-Li, Ryu, and Ken make up the top tier by themselves.

Rose had that crouching MP in Alpha 2 that pretty much beat everything. Like Sagat's crouching HP in Capcom vs. SNK 2 but faster. That was one of the main reasons she was so good. A few of the other characters, like Chun, had some damn good custom combos.

[Wolf Kanno]

I almost forgot Zero from MMX:Command Mission. Incredibly fast and the best damage dealer in the game. Once you unlock his Absolute Zero mode, he can solo most of the game cause he's just ridiculous. Course, Zero is a beast in most Mega Man titles...

Ryogo from Front Mission 3, teamed up the main character, they are unstoppable on his own, he makes you value the power of machine guns since most of his skills and proficiency stems from them. Watching him pull off three special abilities and literally watch him reduce a Wanzer to nothing with just two machine guns is a sight to behold.

Karn from BoF1, he is total bull and the only reason why you would bother with some cast members. For those who don't know, Karn has the ability to fuse with other party members and basically becomes a Swedish Murder Machine, granted he can't fuse with everyone but when he can make the Goldfish guy and Mole kid actually attractive people to bring along, you know something is broken.

I'd also like to second Georg Prime from Suikoden 5 only because I saw him kill a boss, who was at half health and resistant to physical damage, with one attack after something like three parameters all activated at once. He was at low health and activated a move that raises his power, his killer rune activated for a special critical hit, and he went out of turn to do this... It is incredibly rare to see 4 digit damage in Suikoden, at most maybe 1500 but Georg hit for over 5000 with this stunt. There is a damn good reason the game won't allow him to be in your final party until a new game +.

chaos in Xenosaga Episode 1, except for machines (which you rarely fight in this title) and a few Gnosis at the end of the game, chaos is a beast since very few things can resist his innate spirit based attacks, and he gets some truly frightening Tech attacks. chaos has probably been more badly nerfed in later installments than any other character in the series Jr. isn't far behind either since most of his tech attacks hit everything and nothing resists pierce damage.

[Kyros]

Reid in ToD2 is the strongest chara Ive ever seen in a game. He had a move that make omnislash from cloud look like nothing.

[Polnareff]

While everyone's talking about BoF, Capcom mostly got the balance pretty good with BoF3 and BoF4 (well, other than Nina pretty much sucking compared to pretty much the rest of the cast in 3, everyone could at least be used decently under the right masters/skill setups), but they majorly dropped the ball with Dragon Quarter.

Seriously, once Nina gets the Transfer skill, the balance goes out the window completely (as opposed to only thinking of going out the window), especially if Ryu has good equipment. Not to mention the dragon attacks, although those raise the D. Counter and sometimes aren't the most effective way to go about fighting certain bosses (like Dover).

And yeah, Karn is the only reason to bring Gobi or Mogu along. I'd argue that he's the only reason to bring Ox along too (IMO Ox is a boring character in battle, despite his high defense and attack). I've always found it funny how Karn can only fuse with the animal characters even though it's due to story reasons.