Short answers, pulled from the story.
Harald Bluetooth Gormsson was a king of Denmark and Norway who ruled Denmark from around 958 to 986. He was the son of King Gorm the Old and Thyra Dannebod, and he introduced Christianity to Denmark while consolidating control over most of Jutland and Zealand.
Bluetooth wireless technology was named after Harald Bluetooth in 1997, based on the analogy that the technology would unite devices the way Harald united the tribes of Denmark. The Bluetooth logo is a Younger Futhark bind rune combining the initials H and B for Harald Bluetooth.
The earliest written record of the nickname, in the Chronicon Roskildense from around 1140, gives it as blatan. A later twelfth-century chronicle glosses it explicitly as "bluish or black tooth" in Latin, suggesting Harald had a conspicuous dark or discolored tooth. A competing theory holds that the name derived from an Anglo-Saxon term meaning "blue thane" or "dark thane."
The accounts conflict. Widukind of Corvey, a contemporary writer, credits a cleric named Poppa who proved his faith by carrying heated iron without being burned. Adam of Bremen, writing a century later, claims Harald was forcibly converted by Otto I after a military defeat, though Widukind's contemporary account does not mention any such battle.
Harald was deposed by a rebellion led by his own son Swein Forkbeard and died from his wounds around 985 or 986. Adam of Bremen records that he died in Jomsborg, and his body was returned to the Trinity Church in Roskilde for burial, though Swedish archaeologist Sven Rosborn has argued he may be buried near Jomsborg in what is now Poland.
The Ravning Bridge is a structure Harald built at Ravning meadows that is the oldest known bridge in southern Scandinavia. It was five meters wide and 760 meters long, reflecting Harald's use of large-scale public works to extend political and economic control across his kingdom.