Alas, poor Garrick, we didn't know anything about him. His main role in the book is to get knocked off. He's the Chief Justice, which means that he's a VIP under normal conditions. But unfortunately for him, these are not normal conditions. Garrick dies an unremarkable death during the panicked exodus from London. (The brother and the Elphinstones see his carriage in the crowd near Barnet.) What killed him? We don't know. That might be the point. If the Martians weren't attacking, there would probably be newspaper articles about him, his failing health, and his eventual death. But when the Martians come, Lord Garrick is unimportant in comparison.