ungr-endings are quite common in Old Norse names. They probably derive from Old Norse ungr = 'young', and indicate either a pet form of the main name or a patronymic form meaning 'son/descendant of ...'  
They might be closely related to -ingr-endings as well.
An Old Norse variant form (older) is -ungR
An Old Norse variant form is -ungi
A younger Nordic form is -ung
A younger Icelandic form is -ungur