He didn't serve a purpose at all. He appear randomly, for like five minutes, then left. It was at such random times to, and not frequently enough where I would actually consider him an important character at all. And then, "surprise, he's evil?" It was kind of... painfully obvious, Gamefreak. XD Plus when that happened, since he was such a random character, I was more like "okayyy?" then "OMG NO!" so yup, useless character.
They literally could have done SO MUCH more with him, I feel like. He even had a part in the animated game trailer, and watching that now it's kind of weird because he looks like he's a big deal but in reality he's not.