The short-range wireless standard in your ear, named for a tenth-century Viking king and signed in his runes.
Documented
Harald in the specification
In 1997 Intel's Jim Kardach, reading about Harald Bluetooth Gormsson, the king who united Denmark's factions, proposed the codename for a technology meant to unite devices. It stuck. The logo is a bind-rune merging Hagall and Bjarkan, the king's initials.
Assessment: Documented by the people in the room. The runestone at Jelling still broadcasts the original announcement.
Stories
Why the tooth was blue
The colorful version: Harald loved blueberries and stained a tooth. The duller philology: blátǫnn likely meant a dark, dead tooth. Either way a dead tooth named the king, and the king named your earbuds.
Assessment: The etymology is honestly uncertain, which the folk version has never allowed to slow it down.
Interesting claims
Runes as a branding strategy
The observation: a trillion-dollar device ecosystem ships with a Viking monogram as its mark, and almost nobody can read it. The oldest script in your pocket is the one you never noticed.
Assessment: Undeniable once seen. The archive's kind of hidden history: documented, trivial, and weirdly satisfying.
Sources and further reading
Jim Kardach's account of the 1997 codename
The Jelling runestone inscription
Bluetooth SIG logo and naming documentation
Cleasby-Vigfusson, blátǫnn, for the tooth question
Worth asking
A thousand years after the stone, the king's initials are in a billion pockets. Which inscription worked better?