Learn Hardcore Greek: Εκείνος είπε ότι θα έρθει μετά τη δουλειά.

Greek is a pro-drop language, so the verb ending often already tells you who the subject is.
So Είπε ότι θα έρθει μετά τη δουλειά already means He said that he would come after work.

Adding Εκείνος makes the subject more explicit and often adds:

emphasis
contrast
a sense of that person / he in particular

So:

Είπε ότι θα έρθει μετά τη δουλειά. = neutral He said he’d come after work.
Εκείνος είπε ότι θα έρθει μετά τη δουλειά. = He said he’d come after work / That guy said he’d come after work.

What form is είπε?

Είπε is the 3rd person singular aorist of λέω (to say / tell).

So it means:

he said
she said
it said (depending on context, though usually a person)

The aorist is the normal tense for a single completed action in the past.

Compare:

είπε = said
έλεγε = was saying / used to say

So in this sentence, είπε presents the act of speaking as one complete event.

What does ότι mean here? Is it necessary?