The Holocaust was a tragic event that persecuted people for their beliefs and ended up taking 6 million Jewish lives. During the war the Nazi's came up with an idea to terminate all of the Jews called the final solution.
The final solution was to be implemented everyday by the Nazi's. It wasn't just one single action to exterminate the Jews, it was a plan that was made in order to remove the Jewish population.
Adolf Hitler was the main implementer of the final solution, because he was the dictator who said the Jews were ruining Germany. He made the plan but the Nazi's were the actual people to carry out the final solution under Hitler's ruling.
After the Nazi party rose to power over Germany they enforced the segregation of Jews, and forced them into concentration camps. They then began the elimination process commanded by Hitler.