Nier is an unyielding middle-aged man whose wife passed away several years ago. He is left to look after his daughter Yonah whom he loves deeply and strives to provide the best for. Although intimidating in appearance Nier is a kind-hearted man with a strong sense of honor and work ethic. He is a skilled fighter with one-handed swords but comes to master two-handed swords and spears as he relentlessly searches for a cure to the ‘Black Scrawl’ that has afflicted Yonah.
Nier claims to hate killing shades as "it feels like killing a human" but doesn’t hesitate to slay those he’s hired to kill or that attack the village. After Yonah is kidnapped by the Shadowlord Nier develops an intense hatred for shades that borders as an obsession with exterminating them. He even goes so far as to kill the docile shade that lived in the Memory Tree in the Forest of Myth despite its intelligence and ability to reason.
Nier is the ‘Replicant’ of a man from the early 21st century and whose ‘Gestalt’ came to be known as the Shadowlord. When the Shadowlord is slain by Nier it puts mankind on a road to extinction as the intelligent ‘Gestalt’ shades bound to the Shadowlord relapse and their correspondent ‘Replicants’ die of the ‘Black Scrawl’.
Depending on the ending Nier may kill Kainé or sacrifice himself to restore Kainé’s humanity while completely erasing his existence causing everyone to forget he’d ever existed.
In Nier Replicant a slimmer Nier is 16 years old and Yonah is instead his younger sister.
In the book ‘Grimoire Nier’ it states that the forgotten Nier (from ending D) is reunited with Kainé in some kind of spirit world after she encounters the ‘Guardians of the Replicant’ in the Forest of Myth.