The bearded axes most likely appeared in Northern Europe, where they were known since the 7th-8th centuries. The hook or "beard", i.e. the lower portion of the axe bit extending the cutting edge below the width of the butt, provides a wide cutting surface while keeping the overall mass of the axe low. This design allows the user to grip the haft directly behind the head for planing or shaving wood. The "beard" of the axe would also have been useful in battle, for example to pull a weapon or shield out of a defender's grasp. Also the beard is used to climb over the enemy's stockade by both Þrándr in the Eyrbyggja saga and Þórir in the Gull-Þóris saga. In addition to the downward-pulled blade, beared axes were distinguished by a straight upper edge.
Soon they came to Central and then Eastern Europe, where they became widespread. Through Scandinavian mercenaries fighting in the Varangian Guard, the design entered the Byzantine Empire. After the Ottoman conquest of Constantinople, the Sultan's guard adopted axes of similar design to underline their continuity with the Byzantine Empire. In the 15th century, these axes would evolve into single-handed bearded axes with a hammerhead on the head. Through Ottoman influence, these axes would spread to Poland and Hungary, where they would become known as "czekan."

Old Norse skeggøx from skegg 'beard', øx "axe", German Bartaxt.

Axe of iron from Swedish Iron Age, found at Gotland, Sweden (Wikimeadia Commons, public domain). Source Nordisk familjebok (1910), vol.13, Till art. Järnåldern. II https://runeberg.org/nfbm/0251.html

Russian bearded axe. 10-13 centuries. Modern reconstruction by Maxim Baranov, 2011 (Wikimedia Commons, Vladimir Lobachev, Creative Commons CC0 1.0)

Two types of Scandinavian battle axes. Breiðöx (left) and Skeggöx (Wikimedia Commons, public domain). Source Oluf Rygh: Norske Oldsager (1885).