Thane

"I call you out, Magnus, son of Megnin, son of Murbad! Gather your armies if you can, for your head is mine to hew from its neck, just as your grandsire took my father's hand a century hench today!"

- Thrundil Barrelbeard, settling an old debt

Dwarf Thanes are the patriarchs of a Dwarf Clan and a powerful military leader within most Dwarf army. Each Thane has within him a vast experience combating the enemies of their race, often built up over several centuries of constant warfare and strict studies. Dwarf leaders are well tutored in the art of war, learning both from the elders of their own clans and the venerable Runesmiths. When the time comes for them to lead, they will have learnt more than most commanders ever know and will have been tried and tested on the battlefield many times over. This experience and wisdom is reflected upon their beards, a clear indication that the other Dwarfs in the throng would do well to follow their example.

When battle is joined, it is the Thanes, with their finely crafted armor and rune-inscribed weapons who seek out the enemy's most powerful combatants, matching bestial fury or dark magic with courage, honour and honest steel. On several occasions, Dwarf Thanes are known to take command of smaller units of Dwarfs as their own and lead them personally into combat. Most Thanes are readily identified by the large wings that protrude from their helmets.

Source
Warhammer Armies: Dwarfs (8th Edition) -- pg. 34