Task: Question Answering
Input (English): Passage: Fifteen-year-old Ellis Whitman is leaving his home in Tucson, Arizona, for his freshman year at Gates Academy, an East Coast prep school. He leaves behind Wendy, his flaky, New Age mother and Goat Man, a weed-smoking goat trekker and botanist. Goat Man is the only real father  Ellis has ever known, since his biological father, Frank, left when he was a baby.
Upon arriving Gates Academy, Ellis befriends his roommate Barney Cannel, a cross-country runner, and Rosenberg, who usually does not get anything higher than a C in his classes, but is smart enough to sneak in marijuana. Ellis also takes an interest in Minnie, a local girl who works in the school library; his friends often refer to her as a prostitute, according to rumors. Meanwhile, Goat Man and Wendy have been incommunicado, which Barney points out often. On a phone call, Ellis discovers that his mother has a new boyfriend named Bennet, who is rude and disrespectful.
One day, Ellis receives a letter in the mail from his long-estranged father from Washington, DC, requesting for Ellis to spend Thanksgiving dinner with him. Ellis decides to fly to Washington with Barney, who is also having Thanksgiving with his mother there. Ellis finally meets his father and his father's pregnant and kind-hearted wife, Judy. One night, Ellis gets a call from Barney telling him that he is in possession of marijuana. Ellis sneaks out for the night, but Frank finds out that he left. On the way back from his flight from DC, Barney and Ellis get drunk and fight with each other in their dorm room, resulting in a dent in the wall which costs Wendy $700 and Ellis to end up in the school hospital. Afterwards, Ellis begins to get closer to Minnie. 
Question: Who is the actual father of the fifteen year old?
Output (English): Frank.