As Roxie mentioned, this is a fansite. As far as I know, no one here is in any way affiliated with DreamWorks. As much as we'd like to know more about Strider, Spirit's father, we can't make things up about him and claim it to be official. The best source for official information about Strider is one of Kathleen Duey's 'Spirit of the West' books, 'Esperanza'. It's about Spirit's mom, how she gained her freedom, how she met Strider and how they found Homeland.

But feel free to write your own fan story, you can even share it on the Spirit Source (see Fanfic under Fans)!

He actually is mentioned in the books. This is a fan site, we can't make an official movie. Highly doubt that dreamworks will make another movie whilst making some spin off TV series's