It can be very difficult making sure your significant NPCs don't turn into a progression of "Who is this guy again?". Giving them exaggerated traits can help, as we've discussed before, but then you run the risk that anyone who isn't ridiculously exaggerated becomes completely forgettable.

Transcript

Anakin: Master Windu, with respect, you are misinformed. We stayed on board, risking our lives, to land that ship safely. Thousands would have died if not for us.
Mace Windu: They would have?
R2-D2: Yeah, definitely! We reduced the death toll by... oh, half at least.
Palpatine: And they did rescue me.
Mace Windu: Hmmm. Very well.
Mace Windu: Chancellor, you're needed in the Senate. Something big is going down. Apparently.
C-3PO: Oooh! I wonder what it is.
Bail Organa: I'll lay it out for ya. We just got word from Naboo. The Trade Federation's muscling in again. Looks like they're gonna invade.
Anakin: Sorry, Senator...?
GM: Bail Organa from Alderaan. How can you not remember? I made him really edgy and memorable.
C-3PO: Who?
R2-D2: Look, even Sally doesn't remember him.
R2-D2: How are we supposed to remember an NPC who's never even given us a quest?