In Primer there is a secondary character named Thomas Granger that the two main characters Aaron and Abe come in contact with. Apparently he is the father of Abe's girlfriend Rachel and is head of some sort of company.
He is being mentioned as a potential money source for the project and although they decide not to talk to him, later on they find that they are being followed by what is obviously a second Granger from the future in a very bad condition.
What hints are given about what role Granger plays in the whole story and what did most likely happen to him?
Especially the fact that he ends up in a coma (if I recall correctly) makes me wonder, because the side effects of time travel only seem to become noticable after a long time in the box.