Merlin

Merlin, alias Myrddin, Lailoken, etc. is an ancient Brythonic wizard whose fame has survived in legend and song... even as he himself survived in a cave near Alderley Edge, watching over King Arthur and his knights so that they will be able to awaken in Britain's darkest hour and defend it from its enemies.

According to some of the stories, he used to be a soldier in a king's army, or perhaps (particularly given the fact that he is known to play the harp with skill) a bard attached to one, more than a thousand years ago. Driven insane by the horrors of war, he became a wild hermit but acquired the gift of prophecy and other magic. A different source has implied that his madness might stem from the way he came back to life after his death by falling, stabbing and drowning (all at once), which he himself predicted. His magic itself, powerful as it is, seems to be inextractably connected to his madness, though over the ages he learned to maintain control over both... most of the time. This has bled over into a general extreme caution about magic and its use, part of a wisdom won by great personal suffering and not so easily relayed to others. That in turn has contributed to his usually dour and cryptic nature. On the other hand, his efforts to contain his madness had also taught him to be patient with others, no matter how foolish - though, of course, on the few occasions when this dam broke, the results were bound to be cataclysmic.

An added factor appears to be that he knows everything (especially that which is still to come). Not at once, of course, because his mind represses it. But when something brings it to the fore, the weight of the knowledge that is reminded to him all at once can make him more unstable.

The wizard's career at the Court of King Arthur has been copiously if not very accurately or consistently documented. His later life is much more poorly known. He has by all accounts maintained a hermetic lifestyle, keeping well away from civilisation as he watched over the cave. At times, however, local peasants would spot him, or even wander into the cave itself, though they would not be allowed to linger there for long. Aside from his duty, Merlin may also have wished to limit the hazard of his magic. Besides, most outsiders had little to offer to him even when he had a need (John Spencer, in the early 20th century, being a part of the rule rather than an exception, his obstinate materialistic outlook making him useless and tedious to Merlin). Nonetheless, he did take some apprentices over the ages. Most were little more than ignorant local peasants that he taught some basic cantrips to in order for them to be functional assistants for the tasks he needed doing. But there were also talented and exceptional people from the broader world who had somehow managed to find him and convince him to help them, and who he shared his knowledge with and helped in mastering the basics of magic. There was at least one Centurion among them: Manfred von Richthofen, of the 19th century crop; even though later in his life Manfred would renounce magic, he would also stay in touch with his former teacher.

Towards the end of 1913, Manfred would request Merlin's assistance - mainly in the form of life water from the Holy Grail that he was guarding - for his and his friends' research into immortality. When Merlin refused to grant this, wishing to minimise the effect of his magic on the outside world and worried that Manfred was following a dangerous plan that could let life water fall into the wrong hands (something Manfred refused to reassure him about), they parted on amiable terms. A few months later, however, Merlin's watch encountered its greatest crisis since the late Middle Ages, when a mysterious intruder invaded the Cave, blasting through the wards and awakening the knights, causing them to sally forth (and, unbeknownst to Merlin, attack the town of Alderley Edge due to a confusion augmented by supernatural trickery). Outmatched by this attacker, Merlin was forced to divide his efforts and attention between keeping King Arthur alive (his old wounds having been unfrozen) and attempting to delay the invader using his wards and long-distance magics. Fortunately, the confusion with the knights was cleared up with relatively low casualties among the townfolk, thanks in part to the arrival of the young Centurions, including Manfred's pupil, Else Rommel. Merlin had charged these youngsters with infiltrating the cave and evicting his opponent. Aided by Juan Juarez and Merlin himself (though mostly by proxy or at a distance), the Centurions prevailed, even though the intruder turned out to be none other than Dr. Methuselah. Merlin gave out magical boons to those who aided him, returned the knights to sleep and resumed his watch.

...but not before there was one more wrinkle. One of the Centurions, a magical healer named Sarah Hayes, had the temerity to ask him to perform an act of necromancy in bringing her mentor back to life. She pestered him with questions, and maintained eye contact for too long, and did not back off quickly enough. It set him off - as did something else he noticed in Sarah, in her soul, and in her fate during their conversation. Quietly enraged, he did the worst thing he could think of - and showed her some of her future iin her head. This was more than her mind could take, and mercifully she consciously remembered next to nothing when she came to. But the trauma would etch hatred of Merlin into her heart, and set her on the very path he saw. For his part, when giving out boons, Merlin explained that Sarah (then temporarily mute as one of the side-effects of his revelation) was not yet prepared to request hers, but in time she will be and it will be granted. Quite what he meant by that, and whether he took into account the murderous hate that would develop in her with time, remains unclear.