Foaly

Foaly is a fictional character in the "Artemis Fowl" series by Eoin Colfer. He is the technical consultant to the Lower Elements Police (LEP). He is the most intelligent centaur on and under the Earth, considers himself to be an unappreciated genius, and is the inventor of most of the advanced technology possessed by the fairy world, rivaled only by commercial tech giant and former classmate Opal Koboi. Foaly is an avid believer in conspiracy theories.
Little is known of Foaly's earlier life. There is no obvious indication of his age though he seems to be older than LEP (Lower Elements Police) captain Holly Short. In "Artemis Fowl", (first book in series) Foaly is said to have been designing transport pods for over a century, and in "Artemis Fowl and the Lost Colony" Holly states that she is only in her eighties. Foaly is married to a centaur called Caballine, whom he was first revealed to have been dating during the time jump in "Artemis Fowl and the Lost Colony".
Personality.
Foaly is among the most intelligent characters in the series (rivaled only by Opal Koboi) and makes sure the "People" (or Fairies) know it. Foaly enjoys keeping track of various humans, keeping track of human technologies, explaining his technological marvels to others, and researching conspiracy theories (he is quite paranoid about these, to the point of wearing a tinfoil hat). He also seems to like human soap operas, western films, and "Star Wars" as is stated in "The Eternity Code" and the "Artemis Fowl Files". Anything that does not involve his "genius mind" and that the "normal individual" can accomplish he calls "grunt work". This is demonstrated in the second Artemis Fowl book, when Commander Root (head of the LEP) orders him to disassemble and scan various pieces of a shuttle.
In "The Artemis Fowl Files", in an interview with Foaly, he states that he has recently taken up line dancing. In "Artemis Fowl: The Lost Colony" he also shows a habit of singing "Riverbend" songs as he works under pressure, or it could be that he is in love with a female centaur. He also says that he enjoys watching videos or reading articles of himself, an example of the centaur's natural arrogance. He also has a bitter rivalry with Opal Koboi, only because he won their University science fair with his iris-cam, while Opal thought her Koboi wings were far superior, accusing Foaly of winning only because he was a male.
An extremely good friend of Holly's, he sticks by her and helps her out of tight situations quite often. He also has a rivalry/friendship with Artemis Fowl II, and has joked quite often that he'd like to open up the boy genius' brain and finds out what "makes him tick."
Role in series.
In the first book, "Artemis Fowl", Foaly's main role is to set up electronics, research, to supply comic relief and to annoy Commander Root.
Foaly was the only fairy to think that perhaps Artemis Fowl II was one step ahead of the LEP the whole time, which in fact he was. Eoin Colfer further develops Foaly's character and background in the next Artemis Fowl books.
In the second installment, Foaly is framed by former LEP commander Briar Cudgeon and the genius pixie Opal Koboi, who have wrongly accused Foaly of aiding the B'wa Kell (a goblin triad association) in their goal of LEP destruction. However, using Artemis's laptop - which had been left behind in his lab following an earlier visit - Foaly is able to contact Artemis, Butler, Root and Holly for assistance. He subsequently acquired recorded evidence that Cudgeon was planning to betray Opal, which then caused the villains to turn on each other at the last minute.
In the third book, initially, he recognizes the emergency call and sends Holly to investigate, and then coaches her through the arduous healing that ultimately saves Butler's life. Later on, he illegally helps Artemis by giving him fairy technology to use against Jon Spiro and by playing the voice of the C Cube to help deceive Spiro.
In the fourth book, he figures out that Commander Julius Root was killed by Opal Koboi rather than Holly Short as footage seemed to suggest. He uses the Retimager, an invention from the second book that matches images with those on the retinas of one's eyes (allowing Foaly to effectively see what the person has seen, regardless of if they remember it), to discover that the Opal that is in a coma is in reality a brain-dead clone of Opal by determining that the last thing this Opal saw was herself, thus giving Foaly evidence to persuade the LEPrecon to search for Holly Short. She was presumed dead and solely responsible for Root's death, though Foaly helped prove that she had in fact been framed.
In the fifth book, he aides in infiltrating the Paradizo estate and reclaiming the kidnapped demon, N°1, from Minerva. He is also solely responsible for discovering the information about the Paradizos in the first place, mostly because they had erased proof of their existence. He got married during the 3-year period that Holly and Artemis were gone in "The Lost Colony".
Foaly is absent for most of the sixth book, which takes place mostly in the past, but is present at the start when he helps diagnose Artemis's ill mother and reveal the cure, and also at the end when he summons the LEP to protect the Fowl Manor from Opal Koboi.
During the seventh book, Foaly is trapped with Artemis and Holly when they are attacked by Turnball Root, Foaly quickly becoming exasperated with 'Orion', a second personality that Artemis has developed due to his past contact with magic. He also speaks of getting a video game console for 'the kids', insinuating that he and Caballine are parents to at least two centaur children.
In the last book Foaly helps Artemis save the world by sending him the clone of Opal Koboi (who is also known as Nopal). Caballine is targeted for death by Opal's forces; she holds her own in battle but Foaly is needed to save her. The centaur later also creates a clone of Artemis to act as a body for Artemis's ghost, this proves to have saved Artemis's life. It is also revealed in the book how Foaly and Cabaline met.
Inventions.
Foaly has invented many useful things, including: 
There is a short invention guide, including blueprints and images of some of Foaly's better known inventions, in Eoin Colfer's book, "The Artemis Fowl Files". He also is the suspected administrator of 'www.horsesense.gnom', a fictitious fairy website.