Animal personality, also sometimes called temperament, has been investigated in domesticated and non-domesticated species, mammal and non-mammal animals, from foxes and marsupials to horses and sheep. Standardized behavioural tests can be used to assess the phenotype of temperament and have identified large variability within populations of many species. Here, we present three examples that illustrate the importance of temperament variability in animal biology. The first example shows that while