Memory Alpha describes a Dahar Master as:
a Klingon warrior who had reached a legendary status among his peers and subordinates.
And Memory Beta:
Dahar Master is the title given to Klingons, who are the best of warriors and have reached legendary status. These warriors are respected by all and the tales of their exploits are often repeated in stories, songs and operas
To me "master" implies that the warrior has mastered some skill, at the very least "Dahar", whatever that is✝
Does any series or novel cover what Kor, Koloth, and Kang did to achieve this "legendary" status?
✝ Bing Klingon seems to have no translation for the word