Saint Appar is one of the 63 Nayanmar saints known for their bhakti of Lord Shiva. He had converted form Jainism to the worship of Shiva. Saint Appar approached Shiva as a humble servant, and is therefore always depicted with his palms joined in reverence.
He is standing here with a hoe in the crook of his right arm. The hoe is the quintessential symbol which identifies him, and it signifies his readiness to perform even the most menial of services in the temple of his beloved Bhagawan Shiva, including cleaning the weeds that sprang up in the temple.