Why did itachi kill his clan you heard it had something to do with a guy named tobey?

Answer 1

Okay.

===SPOILERS for Shippuden===

Toby is a guy with a spiral mask with only his right eye exposed. However, he is actually Uchiha Madara, who was the strongest Uchiha of his time and who fought the 1st Hokage at the Falls. He has the eternal Mangekyo Sharingan, obtained by taking his brother's Mangekyo Sharingan.

However, the reason why Itachi killed his clan is because his clan was going to have a military coup. As a 4-year-old, Itachi watched many ninja killed in the 3rd ninja war. So, he came to detest war. Were a clan so powerful as the Uchiha to rebel in Konohagakure, all of Konoha would be destabilized and another world war would begin to claim the land of Konoha. So, working as a double agent for the Hokage, Itachi was forced to kill his entire clan. However, he chose not to kill his younger brother whom he adored. Sasuke. Against his orders, he did not, and he begged the 3rd Hokage not to kill Sasuke. Itachi threatened Danzo as well. Itachi told Sasuke a lie so Sasuke would become stronger and would not be killed, and so Itachi left the future of the Uchiha clan to Sasuke.