[quote=Dedonus]
Wait, after just reading the first one (and looking at the Animorph's wiki), the Andalite who gave the Animorphs is Tobias' dad? Please don't tell me that War-Prince Nierefiem-Istriff-Shaylik is secretly one of our character's dads. >.< If that is true, I would put my money on Max. She's the only character who's currently without a father (isnt' she living with her mom and her two brothers).
[/quote]

Elfangor is, yes. It's...complicated. He is Tobias' dad from another timeline, when Elfangor came to Earth to hide the time-traveling device (after the events of the Andalite Chronicles), took the form of a human (Al Fangor) and married Loren. Several years later, the Ellimist interfered and gave Elfangor the choice to return to his people (well, as much of a 'choice' as the Ellimist ever gives), and fixes everything. Everything except the paternal nature of Loren's unborn son, who would be Tobias. 

In the books, this brings Ax and Tobias closer together. They were friends before, but now they realize that they are family. It also helps Tobias explain why his family never seemed to care for him, and why he felt so out of place in life. It's a turning point in the character of Tobias, who is kind of reckless and heedless about his own wellfare before that point.