He didn't want someone who, in one swift action, could kill the remains of the Sith Order by a simple act of betrayal. The Emperor understood that all of the most powerful and intricate Sith abilities and powers ended with him. He could not trust and "outsider" to handle the responsibility of such power, yet he did not want to risk any loss in creating a clone. So, the Emperor had the galaxy searched for the most powerful and deadly women who harbored the ability to not only command the Force, but the Underworld as well. Such a woman had been found, yet her identity and location were never documented. Once that woman proved her worthiness to the Emperor, she gave him the son he desired. Kept a secret for decades, his son was percieved as a trusted General and Assassin until the Emperor decided that the time was right to reveal the truth. Now, Vigo Palpatine has taken his rightful place within the House of Palpatine and continues to serve as protector to his father and sisters. Dark Lord of the Sith, Master of the Underworld and Prince of the Galaxy.