Jonas is the biological son of Mikkel/Michael Nielsen and Hannah Kahnwald. We meet Jonas in the first episode of season 1, alongside his friends Martha and Bartosz after he returns from a mental health asylum, suffering from PTSD after his fathers suicide. Later on, we see the slightly conflicted and awkward relationship between Jonas and Martha, suggesting they had a relationship before he left. After a strange and unusual occurrence in the woods, Mikkel disappears leaving Jonas and his friends distraught, seeking for answers.
Throughout the episodes, we learn about Jonas' ancestors and family tree.
Jonas could be described as an intelligent, coherent, brave individual whos consistency and resilience leads him to revealing most of the answers and mysteries circling the woods.