I whanau a Gates i Seattle, Washington, i te Oketopa 28, 1955. Ko ia te tama a William H. Gates Sr. (b. 1925) me Mary Maxwell Gates (1929<unk>1994). Kei roto i ona tupuna te reo Ingarihi, Tiamana, Irish, me Scots-Irish. I te timatanga o tona oranga, ko tana papa he roia rongonui, a ko tana whaea i mahi i runga i te poari kaiwhakahaere mo te First Interstate BancSystem me te United Way. Ko te tupuna whaea o Gates ko J. W. Maxwell, he perehitini putea a motu. He tuakana ta Gates, ko Kristi (Kristianne), me tetahi tuahine taiohi, ko Libby. Ko ia te tuawha o tona ingoa i roto i tona whanau, engari e mohiotia ana ko William Gates III, ko "Trey" ranei na te mea ko tona papa te "II" he rite tonu. I noho te whanau ki te rohe o Seattle i te Sand Point i roto i tetahi kaainga Karaitiana i pakaru i te wharanga o te wharanga o te wharanga i te wharanga i te wharanga.
ka mahi tonu i te waehere pūmanawa tino