This is Ramanuja Acharya. He is one of the most influential thinkers of Sri Vaishnavism, one of the schools of Vaishnavism. The suffix Acharya refers to Vedic philosophers and teachers and whereas Alwar refers to saints. In general, the period of Alwars preceded that of Acharyas.
Here Ramanuja Acharya is delightfully depicted in a miniature bronze. The patina is deep and there are obvious signs of worship.
He is holding tri-dhanda on the crook of his right hand and his hands are in Anjali Mudra. He is seated in Ardha Padmasana. A multilevel pedestal supports him. He is wearing the sacred thread, visible more clearly in the back view.
Of particular interest are long ears, shaven head, top knot and the muscular body (See the back view).
This bronze is about 8.5 cm in height. It is meant for home worship. The high quality of work and high copper content suggests this Vigraha is from Tamil Nadu. This probably dates to the sixteenth century. The patina, the wear and the bronze loss support that guess.