Brake Pushrod

Stick it back in the master cylinder hook the master to the firewall, and the pedal up. Then pull the brake pedal back towards the drivers seat to pop the rod out.

Or since its already out, If your not keeping the master cylinder, you can put the piston in a vise, heat it up with a propane torch at the end where the rod attaches. Put on your welding gloves and pull the rod out once you smell burning rubber from the retainer.