The door was invented in 649 AD by a Celtic haberdasher named, Isadore Thwack. Prior to his innovation, the portals of every edifice in the civilized world were open to the rain, the wind, and the occasional blood-thirsty marauder. According to the archives at the St. Benedict monastery in Norwich, Isadore, tired of having his wife and daughters ravished by every passing Viking, sought some device that controlled passage through his hovel's portal.
He experimented with many materials from hay to stone. For one reason or another, Isadore rejected each of them until he came to appreciate the attributes of the mighty oak. He crafted an oak "thing" that fit so well inside the confines of his portal that the family was never flooded out and his wife and daughters were ravished less than half the number of times they were before.
News of Isadore's "thing" spread over moor and loch. He began crafting these "things" for his neighbors, then the regional lords, and finally the King himself. The success of his invention not only made him rich and famous, but the Vikings, fed up with battering down these "things" and getting hernias to boot, left the British Isles to plunder virginal Sicily.
In the meantime, Isadore refused to rest on his laurels and spent countless hours ensconced on his 1500-hectare estate finding ways to improve his innovation. In 683 AD, he invented the hinge and the incidence of iatrogenic hernias plummeted a hundred-fold. In 692 AD, came the "Thing-Knob." The invention of the peep-hole had to wait another thousand years with the arrival of a fellow Saxon, named Tom.
Finally, in 717 AD, Sir Isadore Thwack died, rich, content and famous - a victim of the Plague. His majesty, King Elwood II, in an attempt to honor the contributions of this man, declared that a commission be formed for the exclusive purpose of naming the "thing" as a perpetual homage to the creative genius.
The Royal "Thing"-Naming Commission convened for the first time in 719 AD in Greenwich. According to commission records, recently unearthed at the Greenwich Observatory, the first suggestion was to call Isadore's invention, "Thwack." King Elwood II could not endorse that recommendation after spending a week saying such idiotic phrases as, "Close the Thwack" or "Will you open the Thwack? It's getting hot in here" or "Do We hear someone knocking on the Thwack?"
Back at Greenwich, after another two weeks of debates, jousts, and scullery maids, the Sheriff of Shroppshire asked, "Why not call it 'Isadore?'" Upon hearing this latest recommendation, the King slapped the Sheriff in irons, declaring, "Too many syllables. It'll never catch on. Oh, by the way, please detach the good Sheriff's head from the rest of his corpulent body." That last statement, quite understandably, had the effect of stifling the commission's energies. "Izzy" was no longer a viable option.
By 725 AD, the King, tired of the persistent delay, as well as the idiocy of calling the thing "thing," was threatening to draw and quarter every member of the commission, as well as their wives, lovers, children, and pets, unless some solution was discovered. Meanwhile, commission members sought solace in the bosoms of their mistresses and the confessionals of their priests as they imagined their heads decorating pikes on Tower Bridge.
Finally, on July 17, 725 AD, history was made. It was exceedingly hot that day and the King was fearful that steamy, plague-filled humors would advance through the castle portals, rendering him a blackened, bubonic bumpkin. Therefore, he ordered all the "things' to be shut. However, the order was not carried out quickly enough to suit His Majesty.
He commanded again in another fashion to make his point clearer…or so he thought.
"We command you to shut all the Thwacks."
Still no immediate response.
"Close the 'Isadores?' "
No one came.
"The 'Izzys?' "
Finally, bellowing with an anger that only a few ever experienced, King Elwood II commanded that every person in the castle lose his or her head. As mercenaries began carting off the condemned to Tower Hill, one squire exclaimed, well within earshot of the King, "We didn't know what the bloody hell the bloody king was bloody saying. Why doesn't the pompous arse just call the bloody "thing" - "dore" and be bloody well done with it?"
To say that was a "Eureka" moment may sound like hyperbole, but verily, it was a "Eureka" moment since the squire's name was Eureka Jones. Once King Elwood II heard the suggestion, he exclaimed, "Eureka! You've named it. The 'dore.' 'Open the 'dore.' Close the 'dore.' Somebody's knocking on the damn 'dore.' I like it. So simple and yet it memorializes Our dear friend, Isadore. Therefore, We command that henceforth throughout the land, Isadore Thwack's 'thing' will be called 'dore.'"
As a reward, Eureka Jones was knighted that very afternoon and then lost his head that very evening. However, it was impaled on the tallest pike in all of Britain.
How "dore" became "door" is lost to the ages, but most linguists believe that the Irish had something to do with it.