Reginn, often Anglicized as Regin or Regan, in Norse mythology, was the son of Hreiðmarr and foster father of Sigurd. His brothers are Fafnir and Ótr. When Loki mistakenly kills Ótr, Hreiðmarr demands to be repaid with the amount of gold it takes to fill Ótr's skin and cover the outside. Loki takes this gold from the dwarf Andvari, who curses it and especially the ring Andvaranaut. Fafnir kills his father for this gold, but eventually becomes a greedy dragon. Reginn gets none of the gold, but he becomes smith to the king, and foster father to Sigurd, teaching him many languages as well as sports, chess, and runes.

Reginn had all wisdom and deftness of hand. Of his two brothers, he has the ability to work iron as well as silver and gold and he makes many beautiful and useful things. While Sigurd is living with Reginn, Reginn challenges Sigurd's respect in the kingdom. He tells Sigurd to ask for a horse. Sigurd asks the advice of an old man in the forest, and the old man shows him how to get a horse that is descended from Sleipnir, the eight legged horse of Odin. Reginn continues to goad Sigurd, this time into killing Reginn's brother Fafnir. He offers to make a sword for Sigurd, but Sigurd broke every sword Reginn forged for him by striking at an anvil. Sigurd retrieves the broken pieces of his father Sigmund's sword, Gram, and brings them to Reginn. Reginn repairs the sword and gives it back to Sigurd. When Sigurd again tests the blade by striking the anvil, the anvil this time is split down to its base, and when Sigurd places a piece of wool in a stream, the current pushing the wool against the sword was enough to cause the blade to cut it in two. Sigurd is finally very pleased with Reginn's repaired weapon.

Regin (also known as Prax or WarriorPride) is a sophisticated malware toolkit revealed by Kaspersky Lab,Symantec, and The Intercept in November 2014. The malware targets specific users of Microsoft Windows-based computers and has been linked to the US intelligence gathering agency NSA and its British counterpart, the GCHQ.The Intercept provided samples of Regin for download including malware discovered at Belgian telecommunications provider, Belgacom. Kaspersky Lab says it first became aware of Regin in spring 2012, but that some of the earliest samples date from 2003. (The name Regin is first found on the VirusTotal website on 9 March 2011.) Among computers infected worldwide by Regin, 28 percent were in Russia, 24 percent in Saudi Arabia, 9 percent each in Mexico and Ireland, and 5 percent in each of India, Afghanistan, Iran, Belgium, Austria and Pakistan. Kaspersky Lab was unable to determine the attack vector used, and said the malware's main victims are private individuals, small businesses and telecom companies. Regin has been compared to Stuxnet and is thought to have been developed by "well-resourced teams of developers," possibly a Western government, as a targeted multi-purpose data collection tool.