a 'person with a fixed destiny', may be either
one who has committed one of the 5 'heinous deeds with immediate result' (ānantarika-kamma, q.v.), or
one who follows 'wrong views with fixed destiny' (niyata-micchā-ditthi, q.v.), or
one who has reached one of the 4 stages of holiness (s. ariya-puggala).
About the latter cf. the frequent passage:
"Those disciples in whom the 3 fetters (of personality-belief, skeptical doubt and attachment to mere rules and ritual; s. samyojana) have vanished, they all have entered the stream, have forever escaped the states of woe; fixed is their destiny (niyata), assured their final enlightenment."