Little is known about Grandma Tracy's past, and her real name is never mentioned on screen with all the characters, even sometimes her son Jeff, calling her "Grandma". As a young girl, her grandmother took her round London and she travelled on the London Underground, a fact that would prove useful later for International Rescue. She was married to a Kansas wheat farmer but was widowed some time before International Rescue began and helped Jeff bring up his five sons after the untimely death of his wife. During International Rescue's early days she lived alone, near San Miguel, Colorado, however she began to miss feeling useful so decided to move to Tracy Island. Shortly after winning the Parola Sands Race, her youngest grandson Alan Tracy picks her up so she can move to Tracy Island. Unfortunately, a racing competitor of Alan's takes revenge and Alan and Grandma find themselves having to sit still on a bridge spanning the San Miguel River due to a bomb that the enemy has placed under it – should either of them move, the bomb will detonate and the bridge will be destroyed. They are rescued by Alan's brothers, allowing Grandma to see her family's work first hand. She then moves into the Tracy household. As the Tracy matriarch, Grandma keeps her family together, offering wisdom and advice for them and the others in the household, like Alan's love Tin-Tin. It is Grandma who keeps Alan and Tin-Tin together when one of Tin-Tin's old flames pays a visit. Along with Kyrano and Tin-Tin, Grandma takes care of domestic chores in the Tracy household, though she can sometimes be confused by all the technological gadgetry – at one point getting tracking bugs mixed into her apple pie but later being able to work a nuclear oven. Although not an active part of International Rescue, Grandma still plays a role when needed. She has been known to help her grandsons put together equipment they need and it is she who comes up with a solution for a rescue mission at the Bank of England when everyone else is stuck. She also attends the filming of an edition of the Ned Cook Show in which the host thanks International Rescue for saving his life. Grandma has never visited a stately home but hopes to do so one day, especially after meeting Lady Penelope. Grandma's chronology is unclear in that she does not move to Tracy Island until "Move And You're Dead", despite being mentioned in "Sun Probe" and appearing in all four episodes filmed in between. In the original broadcast order, Grandma appears in even more episodes prior to "Move And You're Dead". While the character was intended to debut in "Move And You're Dead" and originally did not appear in any of the previous eight episodes, she was added in when the episode running time was unexpectedly extended from 25 to 50 minutes by order of AP Films' owner Lew Grade, forcing the production to write in new scenes and subplots to pad out the 25-minute episodes that had already been completed.
Grandma briefly appears in the film Thunderbird 6 but has no dialogue. The character is absent from the 2004 live action film, in which she is replaced by a new character called Onaha, who is shown to be Kyrano's wife and Tin-Tin's mother. Grandma returns in the 2015 remake series Thunderbirds Are Go, for which she is voiced by Sandra Dickinson. In the remake, she is one of only three people who know of The Hood. She has a noticeably different personality: she is tougher than the original puppet character, has taken over the role of head of the family following Jeff's disappearance, and is a terrible cook. In series 2, her first name is revealed to be Sally. Carolyn Percy of the Wales Arts Review comments that the remake character's "loving but no-nonsense" personality is in contrast with the original puppet character, who was played as more of a "stereotypical sweet little old lady".
