Complex sentence: Originally formed under the banner of DreamWorks in 1997 by some of Amblin Entertainment's former animation branch Amblimation alumni, it was spun off into a separate public company in 2004.
Split into simpler sentences: Originally formed under the banner of DreamWorks in 1997 by some alumni who used to work at Amblin Entertainment's former animation branch Amblimation. It was spun off into a separate public company in 2004.