Santiago, 18, was named for Santiago, Chile, where he was born in a caravan at the foothills of the Andes mountain range. He travelled the world with his parents, where his parents protested for environmental and political causes. However, he felt estranged and did not care enough for protests. His family was scattered all over the world for months at a time because of their lifestyle.
When the Doctor, whom he had always wanted to meet, was declared dead, Santiago was taken to the UNIT base. There, he met aliens, including the Shansheeth and Groske, for the first time. He quickly made friends with Rani and Clyde and witnessed a plot by the Shansheeth and Colonel Tia Karim to steal the Eleventh Doctor's TARDIS by making a key from the memories of his grandmother and Sarah Jane Smith. Santiago was advised to make some changes in his relationship with his parents.
After a momentary trip in the TARDIS, he left with his grandmother to travel to Norway by hovercraft. (TV: Death of the Doctor) There he was going to meet his parents. His parents wanted to take part in an anti-nuclear rally. (PROSE: Death of the Doctor)
Behind the scenes
- Santiago is one of the few grandchildren of companions to have been portrayed, along with Gordon Lethbridge-Stewart, Donna Noble, Steven Carter, Ryan Sinclair (through marriage) and (to the extent that Brian Williams is considered a de facto companion or "companion presumptive") River Song. He, River Song, Donna Noble, Ryan Sinclair and Susan Foreman are the only known characters whose selves and grandparent have both travelled in the Doctor's TARDIS; he was the first character to have travelled with their grandparent in the TARDIS since the First Doctor's granddaughter, Susan Foreman, in 1965 (2165 in-universe) until Ryan Sinclair and Graham O'Brien with the Thirteenth Doctor.
- Plans were underway for Santiago to return to the screen in the Sarah Jane Adventures Series 5 story The Battle for Bannerman Road, but the passing of Elisabeth Sladen resulted in the story being scrapped.
- It was alleged that Finn Jones was always under the influence of cannabis on set, apparently as he believed it's something Santiago would smoke. However; there is no evidence to prove or deny this.
- Santiago can be seen wearing a necklace-esque chain, and the top of his trousers lower than the top of his underwear (known as sagging), both of which are common styles used by rebellious 13-23 year old boys to show rebellion to what is "normal".
- Santiago and his relative Rio de Janeiro are both named after cities in South America.