Relentless
Re·lent·less
Relentless
a.
-
Unmoved by appeals for sympathy or forgiveness; insensible to the distresses of others; destitute of tenderness; unrelenting; unyielding; unpitying; as, a prey to relentless despotism.
For this the avenging power employs his darts, . . . Thus will persist, relentless in his ire.