Both the name Ragnar and the nickname "Lothbrok", which must not be confused with a surname, had many variations in the accounts of the age. Sometimes his name could be written as Regnar or Regner whereas his nickname/epithet could be written as Lodbrok or Lodbrog.
Ragnar's epithet Lothbrok could be interpreted as "hairy breeches" in the Old Norse language. It could also mean "dirty breeches" according to some.
The epithet is believed to be derived from the breeches he wore while fighting a poison-breathing serpent (or a dragon according to some accounts) in one of the sagas featuring Ragnar Lothbrok.