"Personal computer" can refer either to a small-form computer, in which case the Olivetti P101 was likely the first in 1965 (the PDP-8/E was also a contender), or to a microprocessor-based computer, in which case the Micral N holds that title in 1973.
The Altair, in 1975, was the first commercially successful personal microcomputer.
The Altair, in 1975, was the first commercially successful personal microcomputer.