This is the 13579th most frequent German word.
derjenige
"The one" or "the one who/that."
'Derjenige' is used as a demonstrative pronoun referring to a specific person who knows the answer.
Derjenige, der die Antwort kennt, sollte sie geben.
The one who knows the answer should give it.
'Derjenigen' takes the dative case to agree with the verb 'helfen' and refers to a specific female individual needing help.
Ich helfe immer derjenigen, die Hilfe braucht.
I always help the one who needs help.
'Diejenigen' in plural refers to multiple people being punctual as a condition for entry.