Harald Bluetooth was a powerful 10th-century Viking king who unified Denmark, conquered parts of Norway, and ushered Scandinavia into the Christian era, known for his military might, sophisticated fortifications (like the Jelling Stones, the Trellborg Ring Forts, and bishoprics), and complex legacy as both a pagan warrior and a Christian ruler, leaving behind the famous "Bluetooth" name for unifying technology. His nickname, meaning "dark tooth," likely came from a dead, blue-black tooth, and he was remembered for his strategic genius but also for conflicts with his son, Sweyn Forkbeard, who ultimately ended his reign.

Key Characteristics & Achievements:
The Great Unifier: He united Danish tribes, expanded his kingdom into Norway, and created administrative structures for a unified medieval Danish state.
Christianization: He was one of the first Viking rulers to convert to Christianity, encouraging his people to follow, which marked a major shift from pagan traditions.
Master Builder: He built impressive ring fortresses (like the circular fortresses) and Christian churches, mobilizing vast resources and manpower.
Warrior & Diplomat: He used typical Viking military strength (like raiding and conquest) alongside diplomatic efforts to integrate Denmark into Europe.
Complex Figure: He embodies the transition from the pagan Viking age to the Christian Middle Ages, known for strength but also for conflicts with his son.

The "Bluetooth" Moniker:
Origin: The name likely came from a dark, blue-black tooth, possibly from a dead tooth or eating blueberries/licorice.
Legacy: The name was chosen for the wireless technology because, like the king who united tribes, Bluetooth technology unifies devices.