Aside from being the "Master of Coin" in Game of Thrones, Petyr Baelish was commonly known as "Littlefinger" throughout the HBO series. Aidan Gillen played the conniving character for seven seasons of the show based on George R.R. Martin's A Song of Ice and Fire novels. Littlefinger made a lot of power moves during his arc, but he met his demise at the hands of House Stark, preventing his appearance in the eighth and final season. Though some of Littlefinger's background came into play in the TV show, interesting facts about his past stemmed from Martin's novels, including the story of his background.
In addition to serving King Robert Baratheon's council as the Master of Coin, Littlefinger owned a few brothels within King's Landing. The purpose of the brothels was to gain intel as a spy, seeing as he was one of the most manipulative figures in Game of Thrones. He eventually became the Lord Protector of the Vale after marrying Lady Lysa Tully. The move gave him more power, but Littlefinger actually put the plan in place before the events of the series when he was revealed to be responsible for Lord Jon Arryn's mysterious death. On his path to acquire more honorable titles, Littlefinger took Sansa Stark under his wing, but she eventually recognized his true motivations. When Littlefinger was exposed as the one who started the War of the Five Kings, Sansa had no choice but to have her former mentor executed.
By all accounts, the nickname of Littlefinger had a negative connotation based on the mocking tone. Petyr never carried the best reputation, and the nickname was often viewed as demeaning. It certainly didn't carry the intimidation factor when compared to other Game of Thrones' nicknames like "The Mountain," "The Hound," or "Kingslayer." According to the books, Petyr received his nickname well before the events of the TV series. In fact, Petyr was given the name by Edmure Tully after arriving in Riverrun as a young boy. Based on his small stature, the brother of Catelyn and Lysa began calling the newcomer Littlefinger. The reasoning behind the nickname also had to do with the Baelish's landholdings.
Petyr's Littlefinger Nickname Came From House Baelish's Location
In addition to Petyr's small size, the Littlefinger nickname stemmed from the fact that the family's holdings were the smallest among the Fingers. The area of peninsulas were located east of the Vale of Arryn, protruding into the Narrow Sea. House Baelish owned the smallest peninsula of the Fingers, hence the fitting nickname. Petyr eventually became the primary holder of the keep, but by then, he fully embraced the Littlefinger name. Rather than let it exist as a slight to his background, Petyr took ownership of it as a way to prove how far he had come.
Though Petyr may have taken on a nickname originally intended to be an insult, it wasn't uncommon for Game of Thrones characters to obtain monikers connected to their respective birthplace. Bastards took on surnames based on where they came from, like the case with Jon Snow and Ramsay Snow, two characters from the North. Gendry's surname wasn't accurate in Game of Thrones, but it followed the same system. The Littlefinger name may have held extra significance, but his acceptance of it paid off well into adulthood.