Andreas Avenir is Josie Trent's father and main antagonist of the series. His ultimate goal is to control all of space and time for his own purposes. He is an enemy of the time agency Sarah Pearson and Josie's Clone are a part of.
It is unclear if Avenir is human since he is presumably immortal. He has traveled to an enormous number of different time lines in order to have a child, born of a time traveler, and have that child help him control the universe. As such, he has fathered many different versions of Josie's in different time lines. The number of time lines that Avenir has influenced/manipulated is so great that the repetitive nature of his travels has allowed him to predict events simply because he has lived through many similar versions of events. In all such time lines Josie has always refused to help Avenir.
In the timeline of the series Avenir enlists Vaughn, instead of Josie, to help him control time and space. Sarah had long since known Avenir was at work in her time line and initiated steps to stop Avenir for all time. Her plan was successful and Avenir was trapped in an unknown void for all time.
Other than his plan for temporal domination and fathering Josie, not much is known about the history or nature of Avenir. His ability to time travel at will, the reason he wants to control time, and where he came from, are all unknown.