One of the more prominent heroes of the Fianna Cycle, Caoilte mac Ronan (also sometimes spelled Cailte) was consistently portrayed as the closest and most trusted friend of Finn mac Cumhail. Like Finn, Caoilte was also a member of Clan Baiscne, and some sources refer to him as Finn's nephew, although the details of this relationship are never made clear. His name is thought to have been derived from the words "cael", meaning slender, and "te", meaning fierce.
Caoilte was the greatest runner and all-around athlete of the Fianna, and thus played the role of their chief messenger and scout. Many accounts have him making great journeys in short times, often across the whole of Ireland. One tale tells of an occasion when Mongán, a prince of the Dál nAraidhe clan, contradicted a bard in his feasting-hall. The bard had named the burial place of a certain warrior, and Mongán asserted that he was buried elsewhere. The bard, angered that his telling was being questioned, threatened to satirize Mongán (a grave punishment in the days of oral history) if he could not prove his statement within three days. Mongán sent a messenger to the Fianna, who had men present at the battle and could testify to the warrior's burial place. The Fianna were in southwest Ireland at the time, and Mongán's hall was in east Ulster, quite a distance to be covered. As midnight drew near on the third day, Caoilte vaulted into Mongán's court and told of the death of the warrior in question and his burial place, which mollified the bard. When asked why he was so late in coming, Caoilte replied, "But your messenger only arrived this noon."
The greatest wealth of material on Caoilte comes from the twelfth-century manuscript Agallamh na Seanórach, meaning "The Colloquy of the Old Men". This text tells the story of Oisin and Caoilte going to live in Tir na nOg, the Land of Eternal Youth, after the vicious and bloody Battle of Gabhra decimated the already divided Fianna (see The Life of Finn mac Cumhail 4: Finn's Decline). After residing agelessly in Tir na nOg for many years, the pair got homesick and returned to visit Ireland on a magic horse which preserved their youth. The horse threw them, and when they struck the turf of Ireland they became withered old men. Discovered by St. Patrick, the two recounted the tales of the Fianna for him to record.
Two of these stories in the Colloquy feature Caoilte engaging in foot-races with women of the Tuatha de Danaan. The first has an old hag denying the Fianna passage across a ford at a river near Cruachan. She then makes them a wager, saying that if one of them can beat her in a race, she will allow them to pass, but if he loses he must take her as his wife. The Fianna agree, sure that Caoilte can outrace an old woman. Just as the race begins, the old hag reveals her magical nature to Caoilte, then sprints off ahead of him at blinding speed. Try as he might, he cannot quite catch her. Finn then satirizes him, teasing him as being unable to best an old woman. Shamed, Caoilte makes a series of three bounds that place him ahead of the hag, at which time he draws his sword, turns and cuts her in half as she tries to catch up.
Probably the most famous story about Caoilte takes place during one of the flare-ups which often took place between Finn and Cormac mac Airt, the high king. Because of some rebellion or other that Finn had stirred up, Cormac took him prisoner and held him in Tara. Owing to his agility and athletics, Caoilte was able to get inside to where Finn and Cormac were having dinner together. He then tried to bargain for Finn's freedom, but Cormac would have none of it. Finally, Cormac agreed to set a task for Caoilte to perform but, as it was quite impossible, he shouldn't bother attempting it.
Cormac's task for Caoilte was to collect a breeding pair of every wild animal in Ireland and bring them back to Tara all at the same time. The text then goes on for quite some time describing every animal that Caoilte fetched and from what part of the country and so on. Once he gathered them all together, he brought them to Tara. It was very late at night when he arrived, however, and Cormac said he would not look them over until the morning. Caoilte was given a house with nine doors in which to keep the animals through the night, and it is often they tried to escape. The woodpeckers knocked a hole in the roof and flew away, and by the time he brought them back, more animals had escaped. Regardless, after a long and sleepless night, Caoilte had all the animals still in the house. Cormac ordered them brought to the assembly hall, and Caoilte had to lead the lot of them through the city as the citizens gathered to watch and mock him. The king was delighted with his new collection, but no sooner did he grant Finn his freedom than the entire rabble scattered to the four winds without Caoilte to keep them together.
Finn never forgot the great efforts Caoilte went through to secure his freedom, and there was no man among the Fianna he trusted more. He remained Finn's closest friend and companion until the end of their days. After Caoilte and Oisin recounted their tales to St. Patrick, the Colloquy states that they converted to Christianity and passed away shortly after being baptized by the Saint.