Kakashi Hatake was the sixth hokage who succeeded Tsunade Senju after the fourth shinobi world war. He was the also the jounin sensei to team 7 who all went on to become very accomplished shinobis in their own right. Now back to Kakashi, how strong was he? There is no official power ranking system for shinobis in Naruto and a lot of fights that would have been awesome never happened and this has led to the inability to truly rank shinobis.
An example is how Itachi said if he and Jiraiya were to fight, they would both die and the Sannin are a relatively balanced force but Tsunade is considered weaker than Kakashi, so does that mean that Jiraiya and Itachi are weaker than Kakashi; not by a long shot.
Kakashi is the son of Sakumo Hatake, the white fang of the leaf who was said to be stronger than the Sannin. Kakashi was also a genius in his own right, he could use earth style before joining the academy. He was the first in his generation to be made a Chunin and then a Jounin. He was part of Team Minato who tasked to destroy Kannabi bridge and that turned the tide of war in Konoha’s favour.
He invented the chidori at a very young age and while it was ineffective at the time, he got the sharingan as a gift from Obito and perfected and even went on to create the stronger version, the raikiri. He went on to be feared in different nations and got names like “Kakashi of the Sharingan” and “Kakashi the copy ninja”.
He mastered the Sharingan to a point that even elite Uchihas would be proud of even though he didn’t have the stamina to use it as well mainly due to the fact that he was not an Uchiha. The main reason he was called the copy ninja was because he is said to have copied a thousand jutsus and able to use them because he is one of the few shinobis who can use all five elemental releases and even the first gate of opening.
Kakashi is a very strong shinobi and is also among the elites, while not in the class of monsters like Hashirama, Madara, Naruto and Sasuke, when granted enough power he could still hold his own against the best of the best. It would be interesting to see his role in the boruto anime, either as an adviser to the seventh hokage or reserve combatant in the mold of granny chiyo and Hiruzen Sarutobi. While nothing significant has been said or shown about him in the new anime, we can expect to see him very soon.