Itachi Uchiha is easily one of the strongest characters in Naruto and definitely one of the coolest. His character is loved so much by everyone who watches the Naruto anime and he is in fact compared to a bunch of characters who are in their own right legends in the narutoverse. How strong was Itachi Uchiha? Lets analyse this a bit. Itachi possessed very strong chakra even within the Uchiha and a proof of that was when he mastered the Fire Release: Great Fireball Technique at a young age and at his first try. He awakened the sharingan and mastered it to a level even other Uchihas could only dream of and at the age of 11, he joined the Anbu Black Ops division.
Lets look at the weapons in his arsenal. Lets start with his preferred form of attack: Genjutsu. Itachi skills in genjutsu was so profound that he effortlessly defeated Kurenai Yuhi who was a genjutsu master in her own right. He put Kakashi under a genjutsu that can’t be broken even with the use of a sharingan. He had different types of genjutsu such as the generic genjutsu sharingan (can be done by all who have a sharingan), Tsukiyomi; a power of his Mangekyo Sharingan and Demonic Illusion genjutsu. Next is ninjutsu: Itachi possesses some of the highest skills in ninjutsu in the narutoverse. He is master in three different elemental releases: Fire, Water and Wind and also in Yin-Yang releases. He possesses a susanoo, Not a full body one due to not possessing an Eternal Mangekyo Sharingan He is also a taijutsu able to hold his own against an almost perfect jinchuriki naruto. Now that we have described all his abilities, lets take a look at his battles.
He defeated Kakashi with a look and also Orochimaru (who is a member of the legendary sannin), both very strong shinobi who can use all five elemental ninjutsu, he also defeated Yagura with amaterasu even though that was not intentional as he was getting used to his Mangekyo Sharingan. He said that if he fought Jiraiya (another member of the legendary sannin) they would both die. Itachi had very low chakra reserves and that limited his fighting ability but he made up for it with very refined chakra control. He also possessed considerable strength and speed to enable battle strong characters such as Kisame and blocking an attack from Samehada with just a kunai. He also broke out of Jiraiya jutsu Summoning; Toad Mouth Bind with amaterasu.
Itachi possesses enough skill to be among the strongest Uchihas and is well versed in all shinobi techniques and is also well versed in bukijutsu and in shurikenjutsu. He is often mentioned alongside characters like Minato Namikaze, The third hokage, Madara and even Hashirama himself. I would start an Itachi Versus series that would compare Itachi to a lot of other characters.