Graham Jones from Castlevania: Aria of Sorrow for GBA. That's his second form. He's the boss that determines which ending you get. If you equipped the right souls and defeated him, you'd go on to the canon ending, which can be changed depending on if you got ALL the souls or not.
In the first pic, which is a gameplay screenshot of the second form battle, I just have to say that Soma is so fucked that it's not funny.