1. Third Hokage Influence: The Third Hokage greatly impacted Itachi's growth and instilled in him the will of fire. However, his irresponsible leadership led to resentment from Itachi due to burdening him without revealing his true spy identity before death.

2. Madara Uchiha's Betrayal: Madara worked with Itachi during the Uchiha massacre, but Itachi became hateful when Madara manipulated Sasuke into joining the Akatsuki, which ruined Itachi's plans.

Madara's cautiousness towards Itachi stemmed from his strategic thinking and knowledge as a former Konoha ninja.

3. Danzo Shimura's Extremism: Sharing the same root as the Third Hokage, Danzo went to extreme means by collaborating with Hidden Rain Village, resulting in killing Yahiko, and causing suspicion among his comrades. Itachi carried out the Uchiha massacre on Danzo's orders.

4. Orochimaru's Obsession: Orochimaru, one of the Third Hokage's disciples and a renowned scientific ninja, aimed for immortality and played a significant role in the Fourth Great Ninja War.

Itachi harbored intense hatred toward Orochimaru for jeopardizing Sasuke's life repeatedly.

5. Kabuto Yakushi's Role: Initially an insignificant character, Kabuto became crucial in the Fourth Great Ninja War, much to Itachi's disdain. Itachi despised Kabuto for starting the war as he cherished peace and was willing to annihilate his clan.