| birth_date = {{Birth year and age|1992}}
| years_active = 1998–present
|image=Halfdan portrait (2017) by Nadina Dobrowolska.jpg|caption=Portait of Halfdan (2017) by Nadina Dobrowolska|organization=[[Avalon Larp Studio]]}}
'''Halfdan Keller Justesen''' (born 1992) has larped since 1998, and introduced his parents to larp soon thereafter. He is a trained product designer and currently lives in Copenhagen, Denmark. He organised his first larp in 2018 in collaboration with [[Avalon Larp Studio]], which he is now a member of.