Kakashi is one of the few ninjas in the world who wields a Sharingan who is not actually of the Uchiha clan. In fact, Kakashi had lost the use of his left eye during a ninja mission and was given his eye by the dying hands of his best friend Obito Uchiha.
At first, his eye only contained two tomatoes and therefore was not fully activated or matured yet. It was only after the terrible death of his teammate and friend Rin Nohara that Kakashi's eye completely awakened.
Later on, a lot of what Kakashi grows up to become is the direct result of the amazing capabilities that Obito’s eye has granted him. And for not actually being an Uchiha he has frequently demonstrated — and been commented for — having exceptional proficiency in the use of his Sharingan. So much so that other exceptional Uchiha members have made remarks of him having more skill than that of natural wielders.
One of his most notable achievements is his ability to copy nearly any technique he gazes his eye upon. Which has also led to him being known by many as the famous “copy ninja”.