Vahagn or Vahakn (Armenian: Վահագն), also known as Vahagn Vishapakagh (Վահագն Վիշապաքաղ, 'Vahagn the Dragon-reaper'), is a warrior god in the Zoroastrian-influenced Armenian mythology. Scholars consider him to be either the thunder, or sun and fire god of the pre-Christian Armenian pantheon, as well as the god of war, bravery and victory. He formed a triad with Aramazd and Anahit. Vahagn is etymologically derived from *Warahraγn, the Parthian name for the Iranian god Verethragna, although there are key differences between the two deities.

Vahagn was worshipped at a tripartite temple complex together with his bride Astghik and the goddess Anahit in the district of Taron, on the slopes of a mountain called Karke near the settlement of Ashtishat. After Armenia came under Hellenistic influence in antiquity, Vahagn was identified with the Hellenic deity Heracles, but also rarely with Apollo.

The theonym Vahagn is cognate with Verethragna, the name of the Iranian god of victory mentioned in Avesta, as well as the Vedic Vŗtrahan, the usual epithet of the thunder god Indra. It was borrowed into Armenian from Parthian Varhraγn and developed from the earlier form Varhagn. In the old Armenian calendar, the twenty-seventh day of the month was called Vahagn. Additionally, the planet Mars was called Atraher ("fire-hair") by the ancient Armenians in reference to Vahagn.

Vahagn is mentioned in a number of Classical Armenian written sources. For example, in the history attributed to Agathangelos, Armenian king Tiridates III evokes the triad of Aramazd, Anahit and Vahagn in a greeting to his people: "May health and prosperity come to you by the help of the gods, rich fullness from manly Aramazd, providence from Anahit the Lady, and bravery come to you from brave Vahagn."

Historian Movses Khorenatsi refers to Vahagn as one of the sons of Tigranes (a mythologized composite figure of several Armenian kings in Khorenatsi's history) and records the following song about him:

Երկնէր երկին, երկնէր երկիր,
երկնէր եւ ծովն ծիրանի.
երկն ի ծովուն ունէր եւ
զկարմրիկն եղեգնիկ.
ընդ եղեգան փող ծուխ ելանէր,
ընդ եղեգան փող բոց ելանէր.
եւ ի բոցոյն վազէր
խարտեաշ պատանեկիկ.
նա հուր հեր ունէր,
… բոց ունէր մօրուս,
եւ աչկունքն էին արեգակունք:

Erknēr erkin, erknēr erkir,
erknēr ew covn cirani.
erkn i covun unēr ew
zkarmrikn ełegnik.
ənd ełegan p῾oł cux elanēr,
ənd ełegan p῾oł boc῾ elanēr.
ew i boc῾oyn vazēr
xarteaš patanekik.
na hur her unēr,
... boc῾ unēr môrus,
ew ač῾kunk῾n ēin aregakunk῾:

Heaven was in labor, earth was in labor,
the purple sea was also in labor;
in the sea labor pangs also held
the little red reed.
Along the reed-pipe smoke ascended,
Along the reed-pipe flame ascended.
And from the flame
a red-headed young boy jumped out.
He had (celestial) fire for hair,
and had flame for beard,
and his eyes were suns.

Khorenatsi does not give the rest of the song, but states that it tells of how Vahagn fought and conquered vishaps, which are the dragons of Armenian mythology. This attribute of Vahagn is the reason for his title vishapakagh, meaning "reaper of vishaps" or "dragon-reaper".