Who is the venerable companion whose death caused the Throne of the Most Merciful to shake?

The Companion in question is Sa'd ibn Mu'adh, may Allah be pleased with him. The Throne of the Most Merciful shook at his death. His virtues are many: he embraced Islam at the hands of Mus'ab ibn 'Umair, and his people embraced Islam through his conversion. He was among the first to welcome the Prophet, peace and blessings be upon him, in Medina, and he witnessed Badr and other events with him. Sa'd was martyred by an arrow on the Day of al-Ahzab (the Confederates). He wished to remain to fight Quraysh or to die a martyr after his eyes were gladdened concerning Banu Qurayzah. He did not die until he had pronounced his just judgment upon Banu Qurayzah. He passed away in the fifth year of the Hijra. The Prophet, peace and blessings be upon him, prayed over him, and he was buried in Al-Baqi'.