Madison was a male Starfleet officer who served on the USS Millennium in 2380. He originally served as an officer in the geometrics department before becoming the operations officer or Ops officer on the Beta shift.
When Seven of Nine went to The Nexus bar to obtain a refill for her drink while she was having lunch with Lenara Kahn, Madison attempted to flirt with Seven, obviously unaware of Seven's marital status with captain Kathryn Janeway. The attempt was very unsuccessful.
Paryk told the story of Madisons rude dismissal by Seven to commander Kiara Kelly and lieutentant M'Reek. He described it as Seven cutting Madison into so many pieces that he was surprised that Madison did not leave a blood trail as he left the bar, figuratively speaking of course. (MLN: "Relative Revelations")