On the fourth day of the brahmotsavas the lord deity Lord Malyappa Swamy took a ride as Lord Sri Krishna who is crushing Kaliya on his poisonous heads as he is a king for the evil serpents. This ride is representing that the lord has won over the serpent king and is riding on the Sarvabhupala Vahanam.
The word Sarva Bhupala in Sanskrit represents the meaning of Universal Emperor. As the lord Sri Venkateswara is worshipped by many devotees all around the world so he is given the name A Universal Lord of all the Lords.
All the lords including Lord Shiva, creator Brahma and Indra and the fire god Agni and Yama and Vayu and Nirutthi and Varuna, Kubera and other gods are serving their salutations to the Lord Sri Venkateswara Swamy.
The vahanm on which the god takes a ride resembles that the god id here to help the devotees to fight the bad in them and bring up the good in them.