Professor Xenon is one of the head scientists of the MPA, and is the one in charge of Hydrogen's team. He's usually the one who briefs everyone on the upcoming missions and will contact them if something interesting or dangerous is up ahead. (Don't worry, you can still move around while he's talking to you.) If there's an instance where he can't communicate with his team, or if he spends his time pondering about an off-topic subject, his second in command, Oxygen, will take over where he left off.