Scotland in the Dark Ages could truly be called the Age of the Saints. Ever since the toleration of Christianity in 313 AD by Emperor Constantine III, Christianity in Scotland was set to flourish. Below is a summary of the more important saints and monks of the region. Please note that lives of the saints are controversial and there are many arguments as to what is fabrication and fact; I have put notes to alternative theories in  brackets.
The first saint in Scotland was St. Ninian. He was born in Whithorn on the Solway coast. After travelling to Rome, he made his way home to preach this new religion. He was to stop off and visit St. Martin of Tours and his church had a profound effect on Ninian. He returned to Whithorn. On hearing of the death of St. Martin in 397 AD he resolved to build a similar church in honour of St. Martin. The church he called Candida Casa or "the white house". Indeed the place Whithorn takes its name from this white house.
St. Ninian was the first person to try and convert the Picts to Christianity. He went on a pilgrimage and probably tried to convert the lowland Picts - or the Miathi Picts. He was only partly successful, and the Miathi soon renounced their new religion in favour of their old Celtic ways. [Some commentators argue that St. Ninian lived later, in the early sixth century (c.f. The Saints of Scotland; Alan Macquarrie.) The New Penguin History of Scotland notes that "in the light of the excavations at Whithorn which show 500 AD as a clear horizon for the development of a church there."] St. Ninian's Day is 16th September.
Born in Strathclyde around 354 AD Pelagius was a British monk who denied the Christian theory of original sin. He went to Rome around 380 AD and preached that it was man's own morality and free will that would get him a place in heaven. Not surprisingly, Rome was outraged at his suggestion - for it meant that a good man would not need redemption for the original sin of Adam, and therefore not necessarily need the church. Three times his thesis was tried to be condemned, but each time Pelagius successfully defended his theory, the last just before his death in 418 AD. Only in 429 was the Pelagian theory condemned as heresy, after his death. In Britain, though, the theory took hold, and Rome sent out many monks and saints to combat its teaching.
As his theory was of such importance for the development of the fledging Celtic Church, there follows an extract from Alan Macquarrie's The Saints of Scotland on Pelagius: "He became a teacher and spiritual advisor to a number of well-born Romans, including women (earning him the opprobrium of the misogynist Jerome); his teaching seems to have been based on a moderate, highly moralistic, asceticism. He was opposed to both to the immorality of classical paganism and the extreme asceticism of the Manichaeans, who were opposed to sexual relations in any form and even viewed food with suspicion. His moderate views may have contributed to his popularity among high society in Rome, but led him into conflict with extreme ascetics like Jerome and the church in North Africa. In particular there were disagreements over the questions over the questions of human sinfulness, divine grace and the freedom of the will. Pelagius believed that man is created with the innate knowledge of the divine will and with the power of free choice whether to follow the divine will or not. Thus between the time of Adam and that of Moses it had been possible for some men to lead holy lives; but the failure of the majority to do so had led to the giving of the Law through Moses. This Law enabled men to know the divine will even if they were not prepared to use their innate knowledge. But failure to follow the Law led to the fuller revelation through Jesus Christ. Although Pelagius does not deny to Christ his redemptive or atoning role, he stresses his exemplary role as a crucially important element in Christ's mission. Christ's example shows us that it is possible for man to deny his sinful desires and to live fully in accordance with God's will. There is thus liitle space in Pelagius' scheme for original sin or the need for infant baptism; baptism for him should be a conscious choice on the part of the Christian believer intending to live a good life. Baptism cancels out past sinfulness; but it is not clear why it should be administered to infants, who do not have a baggage of sinfulness to offload. Nonetheless, Pelagius never denied the need for infant baptism."
The Pelagian theory was short-lived in mainland Europe but it set the trend for the British Isle's Celtic Church and the Roman Catholic Church to be very different; a situation not resolved in Scotland till Malcolm Canmore's time over 700 years later.
Palladius was the name of the monk, sent by St. Germanus, to counter the Pelagian heresy in Ireland. This he did not manage, and Ireland remained steadfastly pagan. Not willing to return to Rome a failure, he crossed to Scotland and lived out the rest of his life on the east coast, in Fordoun in the Mearns, where he eventually died. [Some commentators argue that Palladius and St. Patrick are one and the same.] St. Palladius' Day is 7th July.
As already stated elsewhere, St. Patrick was born around Old Kilpatrick around 384 AD. Kidnapped, possibly by Niall (of the Nine Hostages fame) and took to Ireland as a slave. He managed to return home some years later, but a vision appeared and convinced him to go to Ireland and preach the gospel. Having already been in Ireland, he seemed to be the obvious choice of St. Germanus and Rome to replace Palladius in their quest to convert Ireland. That he did, where Palladius failed, is testimony of his character. St. Patrick's Day is 17th March.
Gildas was a British monk, born in Ail Cluathe around 516 AD. He may have been the son of Caw, a deposed King of Strathclyde who may have fled to Wales before returning north again on the succession of Clinoch (Constantine) to once again press his family's claim. Gildas wrote De Excidia Britanniae [concerning the ruin of Britain] in which he calls the kings of Britain 'tyrants'. Written around 540 AD, the title may reflect the impoverished times following the climatic deteriation of 535 AD already mentioned. This book confirms the battle of Badon Hill, a battle attributed to King Arthur which he records as the year of his birth. He died in 570 AD. [Some commentators have Gildas birthdate as 500 AD, and predominately based in Wales or Glastonbury. However the New Penguin history of Scotland notes the probability "that a churchman who wrote to Gildas for advice on monastic discipline, a scholar and bishop by the name of Uinniau (appearing variously as Finnian, Winnin and other permutations) was based in south-west Scotland and had links with early Whithorn." As with St Patrick's Letter to Ceretic, the King of Strathclyde, this points to the probable base of Gildas; otherwise Uinniau would have been unsure whether his letter would have been delivered. In accordance, Stephen Johnson's Later Roman Britain points out Gildas' De Excidia Britanniae has a 'distinct northern bias' and so neglects any mention of the Roman Emperor Constantine III to suit his 'northern' theme. The tradition that his older brothers were killed by King Arthur in 508 suggests that Gildas was born later; for a young Gildas would have surely shared their fate. Ironically given that his brothers probably died in the site of a church, Gildas may owe his to the sanctuary that the church provided.]
In tradition, Constantine arrived in Strathclyde from Cornwall, establishing a church at Govan which still contains his sarcophagus. Gildas writes of his murder of two royal youths, in an uncanny parallel with that of King Arthur killing the sons of Caw, a battle that can be tentatively placed at Cambuslang. It seems likely that Gildas, a native of Strathclyde, was instead referring to this instead of an event placed in Cornwall. I will later argue that Constantine was a king of Damnonia (Strathclyde) not Dumnonia (Cornwall). St. Constantine's Day is 11th March.
St. Thenew was the mother of St. Mungo, and as such shares with him the honour of being patron saint of Glasgow. Her name is commeorated in Glasgow today in St. Enoch's Square in the city centre (Enoch being a corruption of Thenew). The site used to hold a chapel and graveyard in her name. She was the daughter of King Loth (of the Lothians) who guarded her virtue to an extent that no man was allowed near her. Predictably, she fell pregnant when a suitor dressed as a woman seduced her. Loth was furious and tried to kill her, forcing her carriage down Traprain Law, the hill-fort that was his capital. On finding her still alive he cast her off to sea in a coracle, leaving the elements to finish her. Fortunately for her, the currents took the coracle to the Isle of May where monks took care of her. She then went to Culross where St. Mungo was born in 520 AD. St. Thenew's Day is 18th July.
Also called Kentigern, St. Mungo was taught by Servanus, a monk who was a disciple of Palladius. Somehow he became an enemy of Morken, a Prince of Strathclyde - possibly speaking against his intention to take the throne of Gwynedd - and went to Wales. He was to return to Strathclyde on the accession of King Ryderrch, the king who became immortalised in the story of the salmon and the ring. He founded a church at Glasgow, at the site of the present cathedral. According to the Welsh Triads, St. Mungo was King Arthur's chief bishop at Pen Rhionydd; confirmed by Joseph Irving as Dumbarton. He is supposed to have met Merlin at Drumelzier, west of Peebles, where he baptised him in the river. A less than grateful Merlin then prophesied that they would die in the same year. Both died in 612 AD. [Some commentators argue St. Mungo and St. Columba are one and the same. (cf. http://ourworld.compuserve.com/homepages/DavidDale1/Part_1.htm ) ] St. Mungo's Day is 13th January.
Born in 521 AD of royal Irish descent, but banished from there after committing an unknown sin. He fled to Iona, founding a church there. He became involved with the Kings of Dalriada, picking out Aedan as a successor to the throne. Like St. Ninian, he tried to convert the Picts to Christianity. He is said to have met St. Mungo, probably around the western end of the Antonine Wall, where they exchanged staffs. His staff, inlaid with gold, was kept in Ripon Cathedral until the 15th Century. He died in 597 AD. St. Columba's Day is 9th June.
Mirren trained under Comgall of Bangor and founded a church in Paisley in 560 AD. He is said to have worked closely with St. Constantine. Mirren died at the end of the sixth century. St. Mirren's Day is 15th September.
Another Strathclyde saint, probably born in Ail Cluathe in 900. He was said to be related to the royal family of Strathclyde; his biography mentions he was related to King Dovenald (Donald) of Strathclyde. In his lifetime however there were two King Donalds of Strathclyde:- Donald mac Aed (r. 908-925) and Donald mac Eoghain (r. 937-971). There is some dispute as to which king, although as St. Catroe is not mentioned as being related to Constantine of Alba - the brother of Donald mac Aed - it seems likely that he was related to King Donald mac Eoghain.
As a young boy Catroe was placed under the tutelage of St. Bean. After completing his studies he began his pilgramage south in 941, heading first for the town of Loida - at the border between Strathclyde and England, at that time probably sited about the Pennines - then leaving Strathclyde and through England and on to France. He settled in Metz and became an abbot. His wisdom and teachings were revered on the continent and after his death in 971 was declared a Saint.