Dexter Jettster is a Besalisk from Ojom who runs Dex's Diner in the CoCo Town district of Coruscant, and an old contact of Obi-Wan Kenobi's from his years in the field. Ronald Falk voices him in Attack of the Clones (2002).
The scene's actual argument
Obi-Wan brings him the saberdart that killed Zam Wesell because the Jedi Analysis Droids have failed to identify it. Dex recognises it immediately as Kaminoan and explains that the archive cannot see it because the archive only contains what someone put there. Minutes later Jocasta Nu tells Obi-Wan that if an item does not appear in the records it does not exist — and she is wrong, because Kamino has been deleted.
Why it matters
This is the prequel trilogy's clearest statement of its own thesis. The Jedi's failure is not martial, it is epistemic: an institution that has confused its own catalogue for reality, and can be blinded by anyone with the access to edit it. A diner cook with four arms and no Force sensitivity outperforms the Order's entire information apparatus because he has been places and they have not.
The design
Dex is one of the few fully digital characters in the film given genuine physical business — wiping a counter, hauling himself out of a booth, gripping Obi-Wan's hand with one arm while gesturing with two others. The diner itself, all chrome and vinyl, is a deliberate 1950s American import that has become one of the more beloved corners of Coruscant.