Reginar Longneck or Reginar I (c. 850–915), Latin: Rainerus or Ragenerus Longicollus, was a leading nobleman in the kingdom of Lotharingia, variously described in contemporary sources with the titles of count, margrave, missus dominicus and duke. He stands at the head of a Lotharingian dynasty known to modern scholarship as the Reginarids, because of their frequent use of the name "Reginar".