The Dark Factor of Personality (D) is conceptualized as the basic disposition out of which “dark” traits arise as specific manifestations. We herein critically test this conceptualization across nine dark traits in a 4-year longitudinal study with N = 1,261 (n = 470 at the second measurement occasion, employing full information maximum likelihood estimation) adults from the general population. Results strongly support the conceptualization of D. Specifically, D (1) showed high rank-order stability (higher than any of the dark traits), substantiating that it represents a basic disposition; (2) longitudinally predicted individual differences in all dark traits; and (3) accounted for personality changes in dark traits. Additionally, we investigated the pattern of mean-level change of D and the dark traits. In line with the maturity principle of personality development, D (and most dark traits) decreased with age.