Complex sentence: As a Green Lantern, his first duty was to inform Ke'Haan's family of his demise, sharing their grief he vowed to put an end to the one who had been responsible for his death.
Split into simpler sentences: As a Green Lantern, his first duty was to inform Ke'Haan's family of his demise. Sharing their grief he vowed to put an end to the one who had been responsible for his death.