all-timer
/ˌɔːlˈtʌɪmə/Chiefly US
noun
1 Sport (originally and chiefly Baseball ). A sportsperson who has achieved an unsurpassed or unequalled record during their career or who is otherwise considered memorable for some accomplishment.
2An outstanding or classic example of its kind; something considered to have enduring value, significance, or popularity.
Origin
Late 19th century (in an earlier sense). From all-time + -er.