To look after number one is to put your own welfare and advantage above anyone else’s, treating yourself as the priority in any situation. “Number one” here simply stands for oneself, so the phrase is a blunt way of describing self-interest, whether that means watching out for your own safety, your own money, or your own advancement. It is most often used critically, of someone who is selfish or unwilling to help others, though people also use it of themselves, half apologetically, when explaining why they chose the option that suited them best.
What’s the origin of the phrase ‘look after number one’?
The idea behind the phrase is older than the exact wording. Using “number one” to mean oneself goes back to the start of the eighteenth century: in correspondence from 1704-5 collected in Hedges’ Diary, Thomas Pitt wrote of a man that he “doubt not, but ‘tis very careful of number one, and looks no further.” That shows the underlying slang sense of “number one” as “myself” was already in place roughly two centuries before the fixed phrase “look after number one” is recorded, suggesting the idiom built up gradually around this older usage rather than being coined as a complete phrase from the outset.
Green’s Dictionary of Slang treats “look after number one” as one of a family of interchangeable verb phrases built on the same idea, including “look out for”, “mind”, and “take care of” number one, all meaning to take care of oneself irrespective of others. The “look out for” version is attested earlier in print than the exact “look after” wording: Alexander Berkman’s 1912 Prison Memoirs of an Anarchist has a character say “A fellow’s a fool not t’ look out for number one,” showing the phrase family was current in American slang by the early twentieth century.
The exact phrase “look after number one” later became thoroughly familiar in British speech. It was used in a 1982 episode of the sitcom Only Fools and Horses, “Diamonds are for Heather”, written by John Sullivan, where a character is accused of having “looked after number one”. By 1984 it also turns up in an Australian prison memoir, B. Ellem’s Doing Time, which has a character say that surviving inside means you “got to look after number one”. The spread across British, American and Australian sources by the early 1980s shows a phrase that had become common currency well beyond any one place of origin.