I'm not certain how the legend of Santa Claus started. One of the more interesting explanations that I've heard for this yuletide tradition is that Santa is a symbol for the ingestion and worship of the hallucinogenic mushroom, Fly agaric (Amanita muscaria). This theory is based upon the many parallels between Santa Claus and the cultures that have used the Fly agaric as an inebrient. Let's examine some of the evidence cited in support of this notion.

1. Santa wears a red suit with white trim. The Fly agaric is an extremely beautiful mushroom that has a brilliant red cap with white spots
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2. Santa lives at the North Pole. The Fly agaric is a circumboreal mushroom that grows in association (called mycorrhizae) with conifers (Christmas trees!?) and deciduous trees such as birch. This mushroom has been used as an inebrient by inhabitants of these northerly climes, notably in the Kamchatka peninsula region of Siberia. In fact, the Fly agaric was the primary inebrient of these peoples until the 1500's when whalers and soldiers introduced vodka.
    
3. Santa has reindeer. Reindeer are common inhabitants of Siberia and are reported to have a "taste" for Fly agaric. It is also reported, but I question the validity of the reports, that if a person eats the flesh of an intoxicated reindeer, they too will become intoxicated.
    
4. Santa has elves for helpers. Approximately 20 minutes after ingestion of Fly agaric, most people fall into a deep, vision-filled sleep. During this period, the intoxicated individual may receive divine revelations from 'Mukhomor spirits', which are described as small (elves?) people. [As an aside, after awaking, the inebriated person reportedly feels elated and capable of exaggerated physical feats. It has been suggested, although it is most likely incorrect, that the Viking berserkers were inebriated with Fly agaric when they went on their barbaric raids.
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5. Santa enters your house through the chimney. The Mukhomor spirits, which provide divine guidance, enter a dwelling through the smokehole.

Well, is Santa really a hallucinogenic mushroom in cognito? Who knows? But one thing is certain; this hypothesis should initiate some lively conversation on Christmas eve.