Person of Interest File #D-0012
Name: Mr. Dark
Known Aliases: Dark is reported to use many different first names, but apparently never attempts to completely conceal his identity.
Description: Reports vary. Usually stated to be a Caucasian male apparently in his mid-60s, approximately 168 cm (5'6"), 80 kg (180lbs), grey hair.
Date of Birth (If known): No documented information available.
Reason For Interest: Reported to be the senior partner of Group of Interest Marshall Carter and Dark, and to be their primary source of anomalous items.
Rules of Engagement: Sightings and other noted activity to be reported via Protocol 12. [If you are not cleared for Protocol 12, report any information to your direct superior and take no further action.]
Biography: Foundation personnel should be aware that unlike most Persons of Interest, the nature and even the existence of a "Mr. Dark" are in dispute. Reports of a Mr. Dark, generally as a creator/purveyor of anomalous items, have existed for over 500 years [see notes from the Royal Society for the Investigation of the Paranormal for reports prior to 1918]. However, no confirmed evidence that such a person exists as a unique individual is available. The following theories are given relatively equal credence:
1. Dark is a unique individual, who has presumably used anomalous means to extend his life.
2. Dark is a long-lived, non-human entity of undetermined nature.
3. Dark refers to a family long-involved with anomalies. Most reports are, in fact, of activities of various descendants of an original Mr. Dark.
4. "Dark" is not a family name at all, but a title given to various unrelated people.
5. "Dark" is a pseudonym used over many years by different individuals.
6. "Dark" is a fictitious individual to whom others attribute otherwise unexplained anomalous items and activities.
Personnel familiar with the report on SCP-1716, which contains first-hand accounts of an anomalous item created under the direction of a "Mr. Dark," should be aware that this is not independent evidence; all we know for certain is that some individual called himself "Mr. Dark" while engaging in certain anomalous activities.

The following document is an excerpt from Lives of the Famous Alchemists, obtained from a contact with alleged access to “The Great Library of the Ways.” No independent confirmation has been found that this book is accurate, or even exists. Although it may appear to be a detailed reference, we consider it a curiosity and give it little credence. Researcher ███████ has annotated a number of doubtful statements.
Guillaume D'Arc (c1403 - ) a.k.a. William Dark, Benjamin Phineas Dark, Johann Dark, best known as a collector/dealer/auctioneer of the rare and curious, has made significant contributions to the science of alchemy, most notably in the field of life extension.
Guillaume D'Arc (or Darc) was born c1403 in the village of Domrémy, Lorraine, the illegitimate eldest son1 of Jacques D'Arc and an unknown mother. An unusually intelligent child, Guillaume was sent to be educated for the priesthood, but failed to complete his studies due to “ill-suited character.”
Little else is recorded of his life until 1429, when he is known to have been present at the Siege of Orleans with his half-sister, Jeanne. Although not known to have made any significant military contributions, his family connection allowed him to make the acquaintance of one of the Marshals of France, Gilles de Rais, with whom he discovered he had a shared interest in alchemy. A series of experiments took place, ending suddenly when D'Arc fled the area and reappeared in London. It is unclear whether D'Arc had just become aware of the murders for which de Rais is now best known, and disapproved, or if he was a collaborator who thought it was best to escape before their activities became public knowledge. In any event, D'Arc was safely away when de Rais was captured and executed in 14402.
Anglicizing his name to William Dark, he soon set up shop in London as a dealer in "unusual objects" – a euphemism for alchemical and magical supplies. Apparently an alchemist of some skill, a document exists proclaiming him "Consulting Alchemist to the Royal Family" in 14553. However, his pursuit of a method of life extension met with little success until the late 1460's, when he met a fellow experimenter known only as "Beatrice", who claimed to be over 200 years old4. While it is not known precisely what he obtained, it is clear that he found some method to stop (or nearly stop) aging. Despite the obvious value of such a method, for unknown reasons Dark has always declined to share it.
[DATA EXPUNGED]
Dark consistently maintained his business in London, taking on a number of different first names and apparently passing the firm on to a descendant when his lack of aging might attract unwanted attention. Eventually Dark was determined to keep a lower public profile, and in 1871 founded a private club, Marshall, Carter, Dark, and ██████ with three partners. The intention was for Marshall and Carter to be the "public" face of the club, interacting with members, while Dark and ██████ researched and procured "unusual" items and experiences for club members. Dark soon had a falling out with ██████, and the club was known as Marshall Carter and Dark as of 1876. Seldom-seen, rumors that Dark was deceased began to circulate, and no effort was made to discourage them.
At some unknown point, prior to 1900, Dark gained access to the extradimensional space known as the Ways, and became a regular visitor to the Great Library. Although generally disliked by other patrons, Dark has always been careful to follow the rules of the Library, and has never been refused access. Rumors of some influence with the Head Librarian have never been confirmed or disproven.
Desiring to spend more time in the Ways, Dark gained ownership of the former ██████ ████████ ████ and converted it to what is generally known as Dark's Museum (to the few who are aware of it). Although accessible through the Ways, the Museum has been rendered private through the addition of both mundane and anomalous security measures. A visitor claims to have seen an extensive collection of unusual items, as well as research facilities for the creation and study of new (and newly discovered) artifacts. Marshall, Carter, and Dark primarily exists as a means to dispose of items that Dark does not wish to keep for his private collection.
Little is known of Dark's recent research, although an extensive visit to New York City is documented in 1942, apparently for the purpose of developing a technological (as opposed to alchemical) means of life extension. Dark is presumed to primarily reside in the Ways, and is seldom seen elsewhere. Most recently he is rumored to have been at least indirectly involved in a major 2012 assault on "Site-17," a secret facility maintained by the SCP Foundation, with the intent of gaining control of one or more anomalous items or individuals.

Out Of Character note: This tale is not site-wide canon. It is part of this project, which you are welcome to contribute to. It is also not a model Person of Interest file.

Footnotes
1. No historical evidence of such a person exists.
2. Extensive records of the de Rais trial exist, with no mention of D'Arc.
3. There is no evidence that this position ever existed.
4. SCP-545-A claims to have never heard of a Mr. Dark, nor to have shared SCP-545-C with anyone.