OK Tobirama created one of the most powerful justu that has ever been used. Because of the malevolent use of it though people consider him evil. But im here to clear something up.
The Uchiha When an Uchiha loses someone they love they lose their minds and go rouge with their power. Prime example is Madara Uchiha, Obito, Sasuke.
They all lost somebody important to them and gained their MS . The loss of a loved one leads to them becoming corrupted with power and hatred. But what happens if the person would live again?
Tobirama His stern personality makes people think that he hated the Uchiha but in reality he wanted to help them. He confessed to not hating them but not wanting another Madara. So he developed a justu to revive the lost ones of the Uchiha.
EDO TENSEI The reincarnation jutsu that can bring anyone back to life as long as you have a sacrifice. Tobirama created this jutsu not as a weapon but as a peace offering to the Uchiha to help them cope with lost ones. It could revive them and the Uchiha wouldn't be overwhelmed with grief. Then their love would stay surpreme while their hatred would go away.
Sadly he failed because of his death.