Davros’ desire to regain control of the Daleks is one of the leitmotifs of his existence. However, his scheme on Necros was among one of his more insidious attempts to reassert his dominance.
Under the guise of The Great Healer, Davros ran Tranquil Repose, a facility which cryogenically froze people suffering from incurable diseases. The supposed reason for this? To allow those suffering to wait until a cure for these diseases was discovered. The actual reason? So Davros could use the frozen people’s genetic matter to build a new breed of Daleks!
Just to add insult to sickening injury, Davros didn't use every body to make Daleks. He only used those he deemed worthy. The rest were turned into food and sold back to the system where their families lived.
In a cruel twist of fate, when Davros re-emerged after the Time War, he was reduced to being little more than the Daleks’ pet. But don’t feel too much pity for him – he still planned to wipe out all of creation!
In what was his most ambitious plan to date, Davros stole 27 planets – including the Earth – from the universe, planning to use the energy pattern they created to form a reality bomb. On detonation, this bomb would, well, blow up all of reality! It took the Doctor and an alliance of his friends to take Davros and the Daleks down.