Who is lord viththal ?

Viththal’s idol is dark complexioned with protruding eyes and stands on a brick with hands held on the waist. When Pundalik served his parents Lord Viththal was appeased and appeared before him. At that time to avoid any lapse in service towards his parents, Pundalik threw a brick and asked The Lord to stand on it. The Lord stood watching his service with admiration. This idol is different from idols of other deities which wield either a weapon or bestow a blessing with the hand. It depicts Viththal observing everything as a spectator (sakshibhav). The sense organs lie above and the motor organs below the waist. Hands on the waist means the one with the motor organs within His control.{From hindu jagruti}

And our dear baba showed his devotees how viththal manifested in shirdi.Baba said that devotion is the only necessity to get his darshan.