Professor Cid Previa is a non-playable character in Final Fantasy V. Cid is an elderly inventor and scholar from Karnak who researches the Crystals. Together with his grandson, Mid, who researches at the Library of the Ancients, Cid is one of the foremost inventors in Bartz's World.
After researching the Crystals, Cid developed machines to produce more energy from them. With the use of the machines, Karnak became one of the most powerful and prosperous kingdoms in the world. Excessive use of Cid's machinery, however, was damaging the Crystals' structural integrity, and when Cid discovered this, he attempted to shut down the machine in Karnak, but was imprisoned. He is freed shortly after the Warriors of Light are imprisoned. The Chancellor of Karnak, having realized that Cid was right, begs him to shut down the amplification device, and Cid agrees on the condition that the Warriors of Light come with him. The Chancellor protests this, claiming that the party was seen leaving the same meteorite that the monsters currently attacking Karnak poured out of, but Cid remains firm, forcing the Chancellor to comply.
The four fail to save the Fire Crystal, and Cid goes to the pub in Karnak to sulk. The party travels to the Library of the Ancients and meets Mid, who is outraged to hear Cid's state. Mid smacks Cid back to his senses, and using a book he found in the library, the two refit Karnak's Fire-Powered Ship to run without the Crystal or the wind, allowing the party to travel the world to save the remaining Crystal. The ship is destroyed in a whirlpool, but the party make it back to the Library of the Ancients. Cid and Mid tell the party they saw King Tycoon in the desert to the west, and provoke a Sandworm attack to allow the group to enter the desert to search for him.
While the party explores the city beyond the desert, Cid and Mid fly the black chocobo they left behind to its home where they fall into a pitfall, and meet up with the party who has also fallen into a trap. The group find the Fire-Powered Ship, which escaped harm, and an ancient airship, which Cid activates. When the Ronka Ruins lift off, Cid and Mid instruct the party how to infiltrate the vessel and find the Earth Crystal, and retrofit the airship with Adamantite so it can fly up to the ruins. Afterward, the two tell the party how to open a portal to Galuf's World using the crashed meteorites.
In the Merged World, they refit the airship to allow it to transform into a submarine.