Leo Martin is the name of a character makes a single appearance in the Season 3 episode Annie Oakley (episode).
Karl Stern has stolen the Mongoose, a lightweight but powerful laser weapon developed by the FIRM. He needs to sell it to an interested buyer and demonstrates it at a test range for Leo. Leo, a crooked arms trader believes he can sell it to the Eastern Bloc for 10 million (with 10% for himself) but he warns Karl that he needs to arrange for it to be delivered and the borders would be slammed shut. Karl assures Leo that he knows how to do it and can have it in East Berlin in two weeks.
Leo manages to fix the deal with the buyers. It is hot and he himself stands to gain a lot from it. So, although he does not usually get involved in matters of shipment, he makes an exception this time. He tells Stern that he has connections in Mexico. If Stern has trouble with shipment, he can help get it across the border and from there to Cuba. Leo didn't get a chance to test the quality of his connections as Hawke blew Stern and the Mongoose up just a few miles from the Mexican border. What happened to Leo after that is not mentioned.