Creation and design. When Itachi Uchiha is first mentioned by Sasuke Uchiha in the manga, Masashi Kishimoto had not planned out the character's backstory. The only idea he had was to attribute to Itachi some violent action that would have Sasuke wanting to kill him.

Did Kishimoto say about Itachi?

Kishimoto also said in the interview that he only killed Itachi off, because otherwise he would have defeated Madara. ... From the details of his love life which never made it into the manga, to his culpability in causing Naruto to commit murder, here are the 15 Things You Didn't Know About Itachi Uchiha.

What was the original plan for Itachi?

His plan was that, once he had been killed, Sasuke would be hailed as a hero. Itachi never wanted Sasuke to learn the truth surrounding the Uchiha's massacre, and if he did he hoped the memory of a hateful older brother would cause him to not believe it.