I'm going to have to say Cat Grant. For somebody who had an entire season in the beginning credits, she had remarkably little to show for it. Outside of being the local mankiller and throwing an antagonizing line or two at Lois and passes at Clark, she didn't do anything useful. Even Jimmy and Perry forwarded L&C plots even if they didn't really have any themselves. Cat did nothing at all, so I'm not surprised in the least that she disappeared before BatP and was never seen again except in Clark's group picture in HOL.
