Season 1: Like the Mikkel/Michael connection, 2019 Jonas (Louis Hofmann) is actually a younger version of the show's bearded stranger (Andreas Pietschmann). Future Jonas (who is somehow a brunette, even though teenage Jonas is very clearly blond) goes back to 2019 to try to explain what's going on to his younger self and why bringing little Mikkel back from the '80s would have deadly consequences (for instance, Jonas would never be born).
Season 2: Teenage Jonas and future Jonas loop through so many different time periods this season it's hard to keep track. Future Jonas spends most of his time in 2020, trying to save Martha and his friends from the apocalypse, while teenage Jonas travels between 1921, 1986, and 2020 trying to stop the apocalypse all together. In one episode, there are even two teenage Jonases (Jonai?) in 2019 at the exact same moment in time. There's still a lot to learn about the latter half of Jonas' life and how such a sweet kid turned into surly Adam.
- Adam's World: Still stuck in 1888 as his older self and trying to figure out how to get the time machine working the way he saw it in 1921 as a teen, Jonas is introduced to alternate Martha. It's clear that he's being influenced by an older Tannhaus man, who is blind, who introduces him to the concept of sic mundus creatus est, setting him on his path to becoming Adam.
- Eva's World: Although Jonas doesn't exist in this world, he has been taken here by Martha and is introduced to Martha's older self, Eva, who tells him that he and Martha are inexplicably connected between the two worlds. He eventually conceives a child with Martha (though he doesn't know that), and in attempting to protect her, he continues the loops, which results in his death by future Martha's hands. In a parallel reality, Jonas is taken by Adam right after he shoots Martha, and is sent to travel back in time with alternate Martha to stop H.G. Tannhaus's son from ever dying, thus eliminating his existence.
- Origin World: Jonas can't exist in the origin world — Agnes can't be born without time travel, and thus her great-grandson Mikkel, who becomes Jonas's father due to time travel, also can't exist.