Gilbert (or Giselbert) (died 2 October 939) was son of Reginar and the brother-in-law of Emperor Otto I.
In 923, Gilbert and Archbishop Ruotger of Trier invited the Ottonian king Henry I to invade Lotharingia.
Following Henry's death in 936, Gilbert rebelled against the former's son, Otto I in 939, changing his allegiance to the West Frankish king, Louis IV.
Gilbert managed to be practically independent for three years until he was defeated by the army of Otto I in 939 at the Battle of Andernach.
Gilbert was made prisoner, but managed to escape; while fleeing, he drowned trying to cross the Rhine.