Complex sentence: Fifteen years later, he has already founded S.T.A.R. Labs and created a particle accelerator with Caitlin Snow and Cisco Ramon, which exploded as planned, killing civilians and creating metahumans as well as achieving Barry Allen's destiny seven years earlier.
Split into simpler sentences: Fifteen years later, he has already founded S.T.A.R. Labs and created a particle accelerator with Caitlin Snow and Cisco Ramon. As planned, the particle accelerator exploded, killing civilians and creating metahumans as well as achieving Barry Allen's destiny seven years earlier.