Complex sentence: The first comics character of this name was the robot hero Electro, who possessed superhuman strength and could run at 100 mph, a backup-feature star in "Marvel Mystery Comics", flagship title of Marvel's Golden Age predecessor, Timely Comics.
Split into simpler sentences: The first comics character of this name was the robot hero Electro, who possessed superhuman strength and could run at 100 miles per hour. He starred in a backup feature star in "Marvel Mystery Comics", the flagship title of Marvel's Golden Age predecessor, Timely Comics.