¿quién era el hombre que entró? el hombre que entran era mi padre. el hombre que entré era mi padre. el hombre que entraste era mi padre. el hombre que entró era mi padre.

This is the correct answer. In this sentence, hombre is the subject of this sentence and means man. On the other hand, entró comes from the verb entrar and is the conjugation of this verb for the third person singular in the preterite tense. The preterite tense is one of two simple past tenses. It is used to describe actions that took place or were completed at a certain point in the past. Another important word here is era that is the conjugation of the verb ser for the third person singular in the imperfect. The imperfect is used to talk about past actions, conditions, or events that occurred regularly or frequently or that were in progress in a moment in the past.

es is the right