Dúrnir was a dwarf who appears in three Old Norse

Old Norse

Old Norse is a North Germanic language that was spoken by inhabitants of Scandinavia and inhabitants of their overseas settlements during the Viking Age, until about 1300....

 skaldic poems, which suggests that he once was a well-known dwarf 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...

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The most notable poem is Ynglingatal

Ynglingatal

Ynglingatal is a skaldic poem listing the kings of the House of Ynglings, dated by most scholars to the late 9th century.The original version is attributed to Þjóðólfr af Hvini who was the skald of a Norwegian petty king named Ragnvald the Mountain-High and who was a cousin of Harald Fairhair...

:

En dagskjarr Dúrnis niðja salvörðuðr Sveigði vétti, þá er í stein enn stórgeði Dusla konr ept dvergi hljóp, ok salr bjartr þeira Sökmímis jötunbyggðr við jöfri gein.

By Diurnir's elfin race, Who haunt the cliffs and shun day's face, The valiant Swegde Sveigder Sveigðir, Sveigder or Swegde was a Swedish king of the House of Yngling in Norse mythology. He was the son of Fjölner, whom he succeeded as king, and he married Vana of Vanaheimr, probably one of the Vanir. Lured by a dwarf, Sveigðir disappeared into a stone and never came back...  was deceived, The elf's false words the king believed. The dauntless hero rushing on, Passed through the yawning mouth of stone: It yawned it shut the hero fell, In Saekmime's hall, where giants dwell.

A more literal translation: The day-fearing spawn of Durnir warden of the hall betrayed Sveigdir who into stone the rash hero ran after the dwarf. The bright hall of Soekmimir built of giants was enriched by the chieftain`s presence.

He also appears in a list of Dwarves in the anonymous Dverga heiti:

Alþjófr, austri,

aurvangr ok dúfr,

ái, andvari,

ónn ok draupnir,

dori ok dagfinnr,

dulinn ok ónarr,

alfr ok dellingr,

óinn ok durnir.

The third poem is found in Laufás-Edda

Laufás-Edda

The Laufás-Edda was written in the period 1608-9 by the priest Magnús Ólafsson at Laufás on the request of Arngrímur Jónsson.The purpose was to make a systematic and encyclopedic version of Snorri Sturluson's Prose Edda. The myths in Gylfaginning are presented as a series of examples and the...

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Kveða skal hróðr fyr hríðar

hræ-blakks viðum sævar,

drykkr var Durnis rekkum

døkkr, ljósara nøkkvi.

Snorri

Snorri Sturluson

Snorri Sturluson was an Icelandic historian, poet, and politician. He was twice elected lawspeaker at the Icelandic parliament, the Althing...

 also includes Dúrnir in a list of giants 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...

section of his Prose Edda

Prose Edda

The Prose Edda, also known as the Younger Edda, Snorri's Edda or simply Edda, is an Icelandic collection of four sections interspersed with excerpts from earlier skaldic and Eddic poetry containing tales from Nordic mythology...

(Faulkes translation, p.157).

It is possible that the name Durnir is an emendation (or a case variety) of Durinn, mentioned as the father of dvarfs in Dvergatal. Both names mean door

Door

A door is a movable structure used to open and close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates inside of a space....

, or door-warden. The names Durinn og Durnir do not appear in the same texts. The Norwegian

Norwegian language

Norwegian is a North Germanic language spoken primarily in Norway, where it is the official language. Together with Swedish and Danish, Norwegian forms a continuum of more or less mutually intelligible local and regional variants .These Scandinavian languages together with the Faroese language...

 translation of Ynglinga Saga

Ynglinga saga

Ynglinga saga is a legendary saga, originally written in Old Norse by the Icelandic poet Snorri Sturluson about 1225. It was first translated into English and published in 1844....

 from 1900 uses the name of Durinn instead of Durnir.