Lord Shiva is known as Mahadev, as he is the lord of the lords and he has many forms and many names by which he is known in the Indian Culture. Rudra is also one of his names and a form of Mahadev. The Rudrabhishek is performed for appeasing the rudra roop of mahadev, to have his blessings in the form of energy, peace and fulfillment of different desires. The ritual of Rudrabhishek is one of the most ancient and sacred practices amongst Hindus.
Shiva is said to be the eliminator of all the troubles a person may have. He is said to be the greatest guru one may have, so the people who wants to have his blessings and guidance from mahadev perform the holy ritual of Rudrabhisek. There is no one beyond shiva, shiva can bless the person for a happy life forever and at the times of hardship, shiva comes to protect his devotees and for having such powerful blessings people worship Lord Shiva and Rudrabhishek is performed.
The ritual of rudrabhishek can help the person to have the true blessings of Mahadev in the form of happiness and health. ALL the negative energies at his place, in his thoughts and beliefs are transformed into positive ones and in turn the life of the person is changed to positive