This is the 3393rd most frequent Russian word.
пострадавшего
"Пострадавшего" means "the injured person" or "the victim."
In this sentence, "пострадавшему" is in the dative case, singular, masculine, and refers to the affected/injured individual.
Я помог пострадавшему выбраться из машины.
I helped the injured person get out of the car.
This use of "пострадавшего" is in the genitive case, singular, masculine, showing possession or relation to the injured person.
Одежда пострадавшего была порвана.
The injured person's clothes were torn.
Here "пострадавшему" is again in the dative case, marking the recipient of the action (receiving aid).