Anderson is a priest that works for the Iscariot (which from my understanding is a servet service much like hellsing but instead works for the Vatican). His main purpose is to rid the world of the unclean. Because of this fights break out when he and alucard and is the same vancinity, due to the fact in his eyes Alucard is "unclean". On of his special features is that he is a "Regenerator", in other words a priest who cannot be killed(or is hard to kill), which seems to make him valuable to the vatican. His main fighting strategy is using two long sharp 'cleansed daggers' as well as various other religous accesories