A man who claimed to be a historian from the future, but was in fact a 22nd-century inventor stealing technology from the Enterprise-D.
Berlinghoff Rasmussen arrived in A Matter of Time aboard a small time pod, claiming to be a historian from the 26th century who had come to study the Enterprise-D. He questioned the crew at length while they worked to save the planet Penthara IV, and refused to offer Picard advice about the crisis.
Items began vanishing from the ship, and they were found in Rasmussen's pod. He was revealed as an inventor from the 22nd century who had stolen the pod from a real time traveller. He planned to return home and claim the technology as his own inventions, but Data stopped him, and the empty pod went back without him.