back ground info

Jeb Batchelder is a scientist from the 'School'. (A place were scientists conduct genetic experiments on humans.) He is Ari's father, although this did not stop the 'School' from turning Ari into an Eraser. Later Max learns that Jeb is her father too (in the third book).
Jeb helped the flock escape the first time and lived with them for two years, suddenly and inexplicably disappearing afterwards, making the flock presume his death for another two years. He later reappeared at the 'School' when the flock returned, driving Max to hate him with a passion. Seemingly, the scientists did something to him when he returned so Angel can no longer read his mind (though it's possible he possesses some sort of mental telepathy of his own that blocks Angel's). Throughout the series, he keeps insisting that he is still a friend of the flock and wants to help them. Every time he and the flock meet, he reminds Max that everything is a test. Jeb was the person that first informed Max that it was her destiny to save the world. In the third book Max thought that Jeb is the Voice inside her head that she has had throughout the series (in the fourth book she finds out that he isn't).[

from www.wikipedia.com