Okay, Col has been burning a hole in my mind, so I have flushed out some details to help generate hooks to the adventure (he has previous dealings with both wealthy merchants and more scandalous types), spell out his role, and give a sense of where he might know other potential PCs. Feedback welcome.
Teaser
They say Col Tobinson was once a fine ship's mate, aye, able to navigate on maps incomplete and uncharted. Many a ship would hire him, and he was decently well off for his efforts. That was his life for many a year, travellin' upon the Blue Mistress called the sea. Even when he got the white hairs, his eye was keen and his mind sharp.
That all be changed with his last trip on the sea. A tall, black ship, the Midnight Fury was, and paid a pretty penny for Col Tobinson. But something happened on that trip. No one knows for sure, and, well, Col doesn't speak of it much. All thats really known is that he was found, floating upon floatsam, clutching to gnawed remains of the Fury's late Captain, and babbling about "THEM" and "IT CANNOT BE" and similar nightmares.
"Mad" Col was what we be calling him from that day. He gave up the sea, and instead began lookin'. Lookin' for answers to questions only he be know'n. He dove into books upon books, and learnt things that most people wouldn't. They say he can channel some carsed power now, and knows more about the dark secrets of the depths than most, but... he's a mad one, "Mad" Col Tobinson is.
[sblock=Background]Col was born to a sailing family in Sasserine, an only child. He grew up near, on, and under the water. His youth was not remarkable for one of his middling station.
Col had been a sailor and than navigator in and around the waters of Sasserine for almost five decades. His services were used by wealthy captains both legitimate and questionable. Col was well regarded both for his skill and for his discretion. Col also had a keen mind for remembering forgotten grottos, dangerous reefs, and the frightening tales that sailors tell each other. These germs of tales would germinate into the obsession that now grips him.
Col built himself a good bit a wealth during his travels. He was not as rich as some of his merchant captains, but better off than many. It is this money that he burnt through after the incident on the Midnight Fury trying to learn the things he needed so desperately to learn. He started with the books only accessible to the wealthy; when they would not have him anymore, he found lore wherever he could, making bargains with disreputable sorts in town. He as spent almost every coin on seeking occult knowledge, and now lives almost in a destitute existence. No one will hire him for his sailing skills anymore, though a few secretly seek him out on bits of arcane knowledge about the area they will sail through---just enough to sustain his existence.[/sblock]
[sblock=Appearance and Personality]Mad Col is a man in his middle ages who looks like he has not been taking care of himself. His salt-and-pepper hair is in tangles, and his beard would make a dwarf cry. His hands and face show the signs of a life at sea with permanent creases and a deeply burnt tan. Col has piercing hazel eyes, and strangely enough, all of his teeth (apparently, he likes his citrus). He has obviously slept in his clothes a few times.
Col is obsessed with forbidden lore almost to the point of monomania. He sees dark signs everywhere, and always has a comment on the strangeness of the world, peppering his speech with such observations. He is quite erudite in his knowledge, even if he expresses it in a course, semi-educated manner. The one thing he absolutely will not talk about is what happened on the Midnight Fury, and asking him about it is a quick way to boil his anger.[/sblock]
[sblock=Role]Mad Col is really two potential concepts: an
archivist from Heroes of Horror or a bard, both focused on taboo, sanity-bending lore. In both roles, he would be a secondary caster (divine or arcane), party buffer, and master of knowledge (in order of increasing importance). He makes a good "fifth"-character and fits roles that have benefits in Paizo APs. While Col is mad, he understands the benefits of teamwork and sees his pursuit of dark knowledge as a way of protecting others from it; he is by no means a lone wolf/non-team player.
If possible, Mad Col would use some of the taint mechanics from Heroes of Horror to represent his decreasing sanity. This is not vital to his concept and, if too cumbersome, can be dropped.
Col's abilities would focus on Intelligence foremost, with Wisdom and Charisma as needed (the former more important if a bard). He will be a secondary combatant, most likely using a sickle (in its role as a shipboard weapon) and a longspear from the back. I see him as starting at least middle aged if acceptable. He is most definitely not Lawful, most likely Chaotic Neutral.
Mad Col's spells would focus on divinations (to help his mad research) with other spells that fit his flavor (maddening enchantments, summoning of fell creatures to bargain for protection, power, and knowledge, etc.). Feats would be in a similar vein. Knowledge skills would be paramount, with a vestige of some sailing skills that have deteriorated since his madness (a few ranks in Knowledge (geography), Profession (sailor), and Survival).
For PrCs and such, Mad Col would aim for occult lore classes such as the Alienist (CA), Tainted Scholar (HoH), Loremaster (DMG), and similar that benefit his knowledge and buffing abilities. I think Tainted Scholar works best (would have to be slightly modified for archivists), but, as it relies on the taint rules, is of course optional.[/sblock]
To ease forming a party, here are some potential hooks to tie Mad Col to other characters. Feel free to expand.
[sblock=Possible Relationship to Potential Players]
Kalenestarianthalus Floriandin, Gray Elven Beguiler (Voadam) - Kalen would probably know Col after the Midnight Fury incident, or at least heard tales of him in Sasserine. Mad Col may have attempted a conversation once with the elf to see if any of his "tales" held the key to Col's mad quest.
Ozurr Brandskegg (Brogarn) - Could have run across him in Sasserine after his madness; they could have been looking for the same bit of lore on the Watery Gyre of Algenon: Ozurr to learn its spells, Col for the stories of its weakness.
Unnamed Dragon Shaman (hafrogman) - "Sane" Col may have served as the navigator on the ship that brought the shaman to civilization; afterwards, he may have sought out the shaman for the lore of his people.
Nicolai, Human Sorcerer (Land Outcast) - It is unlikely Col served on The Serpent, but he may have been on a ship predated by it.
Damash Eriskan, Aventi Priest (Tonks) - Upon reaching Sasserine, Damash may have heard of a madman that studies the occult lore of the isles and sought him out.
Unnamed Hadozee Swashbuckler (Tonks) - No idea.

Col would definitely be interested in such an oddity.
Valin Kholgard, Human Scout/Future Pilot/Captian (A'koss) - Valin may have trained under Col before the Black Fury incident for piloting skills and formed a friendship then; Valin may feel sorry or scorn for his former teacher now.
Unnamed Gnome Alchemist (scranford) - The alchemist may have been on board a vessel that "Sane" Col worked on or been the subject of one of "Mad" Col's investigations for knowledge.
Anar Tovanni, Rogue/Fighter (Rhun) - Not enough background to speculate.
Vakra Quinn, the Half-Elf Warlock (rowport) - May have crossed paths in the town before and after the Midnight Fury incident; if Vakra associates with one of the less reputable groups in Sasserine, he may of encountered a desperate Col looking for odd lore.
Unnamed Barbarian (Ringmereth) - Col may have been on the vessel the barbarian used to flee to civilization after his escape.
Akagi Harishia, Shugenja (JDragon) - Col would surely seek out this odd traveler for potential tales that could hold the key to the secrets he seeks, though Col would likely upset the outlander's sensibilities.
Irisa, Half-Elf Druid (Tabbycat) - Col may have tried to delve Irisa's druidic secrets to add to the mysteries he studies.
Sebrina Cardell, Sorcerer (Saloric Windrunner) - It is likely that Col was employed by Sebrina's family before the incident and they may have met each other then; she could feel pity or disdain for his current state.[/sblock]