Original: Dragon Ball Z manga, volume 11, chapter 131 Mecha Frieza Physically ruined while caught in Planet Namek's explosion after Goku defeats him, what remained of the still-living Frieza was salvaged and rebuilt with cybernetic enhancements by scientists under the order of King Cold.
Simplified: Mecha Frieza Physically ruined while caught in the Planet Namek's explosion after his defeat, what remained of the still-living Frieza was salvaged and rebuilt with cybernetic enhancements by scientists under the order of King Cold.