Cid

Cid is a character originally from Final Fantasy VII, who makes an appearance in all three Kingdom Hearts games. He is voiced by Chris Edgerly in the English version of Kingdom Hearts II (having never spoken outside of text boxes in the original) and Kazuhiro Yamaji in the Japanese version. Cid will participate in the game Kingdom Hearts coded.

Kingdom Hearts
''Owner of an accessory shop in Traverse Town. A highly skilled engineer and a first-rate pilot. When the Heartless invaded his world, he escaped to Traverse Town on a gummi ship he'd built himself. He is an expert on gummi ships.''

"Final Fantasy VII"

Kingdom Hearts: Chain of Memories
A gifted pilot who saved Leon and the others from the Heartless when they were just children.

Cid lives in Traverse Town now.

Kingdom Hearts II
Final Fantasy VII

''An engineer, tech wizard and first-rate pilot. He met Sora as a castaway, while he was running a shop away from his hometown.''

Now that he's back home, Cid is an active member of the town's Restoration Committee.

Kingdom Hearts
In the original Kingdom Hearts, Cid is one of the first characters that Sora befriends in Traverse Town. He first owns an accessory shop in the center of the town's 1st district. Cid sends Sora out to deliver an old, broken book (The Adventures of Winnie the Pooh) to Merlin. Later on he owns a shop which specializes in Gummi Ship parts. This is true to his Final Fantasy VII counterpart, as he is an expert on air travel. In fact, most incarnations of Cid in the Final Fantasy series have been associated with airships and mechanics. Like Leon, Merlin, and other important characters met in Traverse Town, Cid was originally from Radiant Garden.

Kingdom Hearts: Chain of Memories
A memory-based version of Cid appears in Chain of Memories, in the memory-based version of Traverse Town.

Kingdom Hearts II
In Kingdom Hearts II, Cid is a member of the Hollow Bastion Restoration Committee who resides in Merlin's home with the other Radiant Garden characters. Cid seems to have a rivalry with Merlin because Cid favors technology over magic while Merlin favors the exact opposite. He is a computer expert, and manages to create a program which helps Sora and Tron defeat the Master Control Program.

Kingdom Hearts coded
Data Cid is looking for Data Huey, Dewey, and Louie when Sora saw him having a problem he tries to help him find the triplet. After defeating the source of the Block Corruption Data Guard Armor and finding the triplets he ask Sora to give him a Haste Drink and trade for Sora a Glow Bangle.

Trivia

 * He is one of five Final Fantasy characters featured to not have a featured weapon, the others being Aerith and the Gullwings. He is also the only Final Fantasy character not seen participating in any battle, whereas Aerith served as healer and the Gullwings managed to defeat an Armored Knight through a team effort. If he does have a weapon, then it is likely his custom-made spear. (However the Kingdom Hearts manga briefly showed him attacking Heartless with a flamethrower. the backpack he wears during this scene is also a cameo of the main weapon of the Cid from Final Fantasy Unlimited)
 * Though each Final Fantasy game each has had its own Cid since Final Fantasy II (and remakes of the original Final Fantasy mentions a Cid as well), the Cid of the Kingdom Hearts series is that of Final Fantasy VII, Cid Highwind. As a Cid, he bears the trademark of his association with machinery and airships, or gummi ships in this case. Like Cid Highwind, the Kingdom Hearts Cid is a pilot and is rather uncouth behavior with a good heart. However, what is not retained is smoking habit, thus the lack of the box of cigarettes strapped to his goggles and his trademark cigarette in his mouth which is replaced by a toothpick to produce a similar image, and more importantly, his signature foul mouth, with many of these foul words replaced by symbols in the English translation. In addition, his attire resembles neither his original design or his appearance in Final Fantasy VII: Advent Children.
 * There was no voice actor for Cid in Kingdom Hearts. Instead, he is only seen talking in text throughout the whole game. In Kingdom Hearts II, his voice actors in Final Fantasy VII: Advent Children, Kazuhiro Yamaji and Chris Edgerly, reprise the role.