Is altair in assassins creed 2

Indeed he is. Altair isn't only the main character who was involved in the beginning of the storyline, he appears throughout the series. However as you should know, the main character II, Brotherhood, and Revelations is Ezio Auditore da Firenze.

In Assassin's Creed II, Desmond Miles collapses involuntarily after going into Eagle Vision due to prolonged use of the Animus. He has a dream of Altair and Maria (his lover), during this period you can play as Altair. You can have a fight with one of the classic templar knights too with the new combat system which is quite fun. The dream ends when you have to take Leap of Faith into a haystack.