Ridill is weapon that appears in Norse Mythology

Norse mythology

Norse mythology, a subset of Germanic mythology, is the overall term for the myths, legends and beliefs about supernatural beings of Norse pagans. It flourished prior to the Christianization of Scandinavia, during the Early Middle Ages, and passed into Nordic folklore, with some aspects surviving...

, possessed by the dwarf Regin

Regin

Reginn, often Anglicized as Regin, 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...

.

Under the guidance of Regin, Sigurd

Sigurd

Sigurd is a legendary hero of Norse mythology, as well as the central character in the Völsunga saga. The earliest extant representations for his legend come in pictorial form from seven runestones in Sweden and most notably the Ramsund carving Sigurd (Old Norse: Sigurðr) is a legendary hero of...

 killed Fafnir

Fafnir

In Norse mythology, Fáfnir or Frænir was a son of the dwarf king Hreidmar and brother of Regin and Ótr. In the Volsunga saga, Fáfnir was a dwarf gifted with a powerful arm and fearless soul. He guarded his father's house of glittering gold and flashing gems...

, Regin's older brother that had killed their father Hreidmarr and monopolized his treasure. Afterward, Fafnir's heart was cut out and roasted for Sigurd and Regin to eat. According to Poetic Edda

Poetic Edda

The Poetic Edda is a collection of Old Norse poems primarily preserved in the Icelandic mediaeval manuscript Codex Regius. Along with Snorri Sturluson's Prose Edda, the Poetic Edda is the most important extant source on Norse mythology and Germanic heroic legends, and from the early 19th century...

, Regin used Ridill to rip out Fafnir's heart. But in the Volsunga saga

Volsunga saga

The Völsungasaga is a legendary saga, a late 13th century Icelandic prose rendition of the origin and decline of the Völsung clan . It is largely based on epic poetry...

, it is Sigurd who used Ridill and cut out the heart at that occasion.

Incidentally, in the Skáldskaparmál

Skáldskaparmál

The second part of Snorri Sturluson's Prose Edda the Skáldskaparmál or "language of poetry" is effectively a dialogue between the Norse god of the sea, Ægir and Bragi, the god of poetry, in which both Norse mythology and discourse on the nature of poetry are intertwined...

the name of Regin's sword is Refil instead.