Ulrich Nielsen is a headstrong police officer. He is married to Katharina Nielsen, but has an affair with Hannah Kahnwald. Following the disappearance of one of his children, Mikkel Nielsen, he fiercely attempts to find him, becoming entangled in Winden's mysteries.
Rebellious and resentful as a teen, Ulrich grows to become a carefree and loving (albeit unfaithful) family man. However, after his son Mikkel disappears and memories of his brother's disappearance resurface, he becomes unequivocally committed to finding them. Eventually, he turns reckless and obsessive to the point of attempting to murder a child.
Ulrich is seen as a troublesome youth in 1986. The disappearance of his brother, Mads Nielsen, leaves him deeply resentful, which he seemingly channels in random acts of rebellion.
He becomes friends with young Hannah Kahnwald after both meet during a stormy night at a bus stop. Often hanging out together at Winden's high school, Ulrich is oblivious to the girl's romantic feelings towards him as he starts dating Katharina Nielsen.
Jealous of the relationship, Hannah later presents a false testimony to Egon Tiedemann accusing Ulrich of rape after seeing him and Katharina have sex. Consequently, Ulrich spends several days in jail as Hannah's story was corroborated by the fact Katharina fell and hurt herself in an unrelated incident.
After Katharina herself explains the situation, Ulrich is released and his mother, Jana Nielsen, vows to get Egon off Mads' case following the unjust arrest.
Ulrich leads a seemingly uneventful life as a police officer and family man, being now married to Katharina and having fathered three children: Mikkel Nielsen, Martha Nielsen and Magnus Nielsen. In secret, however, he maintained an affair with Hannah which he breaks off regretting cheating on his wife.
Following Mikkel's disappearance, Ulrich starts fiercely searching for him. In his investigation, he slowly begins to note several similarities between his son's and his brother's cases, which eventually leads to learn the body found in Winden's forest was, in fact, Mads'.
As his marriage and personal life begin to deteriorate, Ulrich comes to conclude Helge Doppler is somehow connected to the disappearances occurring in Winden.
After following an old Helge through the forest, Ulrich ends up finding the wormhole and traveling back to 1953. There, he meets Helge while still a child and, convinced to change the future, attempts to kill him, paradoxically setting in motion the events that would lead Helge to become Noah's henchman.
Jailed by the police as the culprit for the recent crimes reported in Winden, Ulrich is last seen locked in a prison cell.