Þorgils gjallandi (1 June 1851 – 23 June 1915) was an Icelandic author born in the hamlet of Skútustaðir by Mývatn, a lake in the Skútustaðahreppur rural municipality.
His name at birth was Jón Stefánsson, but he adopted the name "Þorgils gjallandi" as his nom de plume.
The name is taken from the epic Egils Saga.
The original Þorgils gjallandi was a servant in the household of Þórólfr, who was the elder son of Kveldúlfr and the paternal uncle of Viking poet Egill Skallagrímsson; gjallandi is not a proper name but an epithet meaning "the yelling" or "the bellowing."
Many of his stories relate the achievements of nonconformist people who lacked the professional standing to silence their antagonists.