Without mercy or pity:
— A monster of remorseless cruelty.

synonyms: pitiless, ruthless, unpitying.

Roget 919: revengeful, vengeful; vindictive, rancorous; pitiless etc. 914.1; ruthless, rigorous, avenging.    unforgiving, unrelenting; inexorable, stony-hearted, implacable; relentless, remorseless.    aeternum servans sub pectore vulnus [Lat.]; rankling; immitigable.    ... show more

Roget 951: impenitent, uncontrite, obdurate; hard, hardened; seared, recusant; unrepentant; relentless, remorseless, graceless, shriftless^†.    lost, incorrigible, irreclaimable.    unreconstructed, unregenerate, unreformed; unrepented^†, unreclaimed^†, unatoned.    ... show more

Polish: bezwzględny