Aleksander role is very crucial in season 2 , but since the mystery of his past is what brought clausen to winden . who is boris Niewald really ? Could aleksander/boris be the child of martha and jonas ? 

The key to this theory might be Boris gun ?the one that Jonas' mother Hannah held onto for so long. Adult Jonas took the gun from Hannah and used it to force Martha to go to the bunker; some time later, the same gun ended up in the 1920s in the Sic Mundus headquarters, which Noah tried to use to kill Adam, and was used by Agnes to kill Noah after he failed. Then the same gun was used again by Adam to kill Martha in the final moments of Season 2. If everything is a loop, how did that gun return from Adam's hands in 2019 to Boris' as he arrived in Winden in 1986? Did Adam give the gun to his own son before sending him through time ?

But if Aleksander/Boris is the son of Adam and Eve, knowingly or unknowingly, how did he end up arriving in Winden in 1986? It's possible he was sent back in time by one or both of them to fulfill his role in inadvertently triggering the apocalypse. In fact, alterna-Martha's fingerprints are all over this particular manipulation, literally.