He started a genocidal movement known as the Holocaust. He believed and convinced others to believe that the Jews were tearing Germany apart. Hope this helps!
There is an endless list of answers towards this question my most important 3 are
1: he ordered huge advancements in the health and technology field that we still use to this day rather that be in computers, rockets, or medical science
2: he pushed for a land grab increasing the size of his country by huge amounts which would in turn increase their power and income from taxes
3: he believed non Aryan race members to be of lower quality, non pure, and cause of the failure from WWI. Even though he did not meet the requirements of blonde hair or blue eyes he still wanted souly that and expected it to happen further down the timeline
