Complex sentence: Elastic had previously created the title sequences for "Rome", "Big Love" and "Carnivale" for HBO, and they were approached by Carolyn Strauss of HBO with whom they had worked on these shows to create the title sequence for Game of Thrones.
Split into simpler sentences: Elastic had previously created the title sequences for "Rome", "Big Love" and "Carnivale" for HBO. They were then approached by Carolyn Strauss of HBO with whom they had worked on these shows to create the title sequence for Game of Thrones.