He is a young man, Not much is mentioned about his appearance.
While Yuan Kun has an extremely ruthless and arrogant personality. He is not completely without reason as shown by the fact he was willing to excuse Yang Qi of his past behavior if he joined the Gentleman's Society.
He is a genius at cultivation who sixty years ago while only an elite student, Traveled to the northeast with nothing but his halberd to execute the seven evil cultivators known as the Seven Scourges of the Sea of Trees.
The Seven Scourges of the Sea of Trees were evil villains who took over the northeastern jungle sixty years ago. They practiced a wicked energy art in which they killed people to collect their souls. They committed every crime imaginable. Eventually, they reached Quinary Lifeseizing and formed evil true energy vestiges and acquired the remnants of an ancient, villainous encyclopedia called the Sutra of Myriad Evils.
Yuan Kun did this while only a Quaternary Lifeseizer. In comparison, The Seven Scourges were all Quinary Lifeseizers.