Thomas Dodd was a citizen of the planet Mondas. He lived in a time when the planet had separated from the Sol System and was heading towards the dangerous Cherrybowl Nebula. A self-described "purveyor and fitter of necessary bodily parts," he dealt in selling organic body parts, which were in high demand due to the often temperamental artificial organs created by the Mondasian Committee.
On meeting the Fifth Doctor, Dodd planned to kill the Doctor and sell his body parts as merchandise, noting the Doctor's health and that the stranger had no identity papers. Dodd offered him a drink and was refused. Dodd fled with the Doctor after he antagonised one of the Committee Police, becoming a fugitive in the process. He reluctantly followed the Doctor to investigate the police convoy operating after curfew hours. From the bell tower of the abandoned Church of Former Day Souls they spotted Committee trucks transporting corpses from the graveyard to be used in the Central Committee's nutrient supply. After narrowly avoiding being arrested, Dodd and the Doctor ring the church bells to alert the populace to the Committee's machinations.
When the Doctor asked him to help break into the Committee's palace, Dodd finally tricked him, locking him up in a cold storage unit in his shop, intending to gain a fresh supply of stock. The Doctor was rescued by Doctorman Allan and Dodd was captured to be used as a medical test subject. He was later converted into one of the newly improved Cybermen. (AUDIO: Spare Parts)