The given name Haraldr (also Haralldr) is the equivalent of Old English Hereweald, Old High German Heriwald, from hari "army" and wald- "rule".

[3] Harald's name is also inscribed on the so-called Curmsun disc, rediscovered in 2014 (but part of a Viking hoard previously discovered in 1841 in the crypt of the Groß-Weckow village church in Pomerania, close to the Viking Age stronghold of Jomsborg), as +ARALD CVRMSVN + REX AD TANER + SCON + JVMN + CIV ALDIN, i.e. "Harald Gormson, king of Danes, Scania, Jumne, [in] Bishopric of Aldinburg [de]".

The byname is given as Blachtent and explicitly glossed as "bluish or black tooth" (dens lividus vel niger) in a chronicle of the late 12th century, Wilhelmi abbatis regum Danorum genealogia.

All five fortresses had similar designs: "perfectly circular with gates opening to the four corners of the earth, and a courtyard divided into four areas which held large houses set in a square pattern.

He came to the help of Richard the Fearless of Normandy in 945 and 963, while his son conquered Samland, and after the assassination of King Harald Greycloak of Norway, managed to force the people of that country into temporary subjugation to himself.

When Styrbjörn brought this fleet to Uppsala to claim the throne of Sweden, Harald broke his oath and fled with his Danes to avoid facing the Swedish army at the Battle of Fýrisvellir.

[12] The Curmsun Disc, found in Groß-Weckow, Pomerania, (after 1945 Wiejkowo) is inscribed with "ARALD CVRMSVN" (Harald Gormson), calling him, in abbreviated Latin, "king of Danes, Scania, Jomsborg, town of Aldinburg".

[13][11][14] From 1835 to 1977, it was wrongly believed that Harald ordered the death of the Haraldskær Woman, a bog body previously thought to be Gunnhild, Mother of Kings until radiocarbon dating proved otherwise.

[17] King Harald Bluetooth's conversion to Christianity is a contested bit of history, not least because medieval writers such as Widukind of Corvey and Adam of Bremen give conflicting accounts of how it came about.

[21] However, Widukind does not mention such an event in his contemporary Res gestae saxonicae sive annalium libri tres or Deeds of the Saxons.

[23][24] The story of this otherwise unknown Poppo or Poppa's miracle and baptism of Harald is also depicted on the gilded altar piece in the Church of Tamdrup in Denmark (see image at top of this article).

[25] Adam of Bremen's claim regarding Otto I and Harald appears to have been inspired by an attempt to manufacture a historical reason for the archbishops of Hamburg-Bremen to claim jurisdiction over Denmark (and thus the rest of Scandinavia); in the 1070s, the Danish king was in Rome asking for Denmark to have its own arch-bishop, and Adam's account of Harald's supposed conversion (and baptism of both him and his "little son" Sweyn, with Otto serving as Sweyn's godfather) is followed by the unambiguous claim that "At that time Denmark on this side of the sea, which is called Jutland by the inhabitants, was divided into three dioceses and subjected to the bishopric of Hamburg.