  We present a long-term and intraday variability study on optical
multiwaveband ($U\!BV\!RI$) data from the blazar AO 0235+164 collected by
various telescopes for $\sim$44 years (1975--2019). The blazar was found to be
significantly variable over the years in all wavebands with a variation of
about six magnitudes between its low and active states. The variations in the
different wavebands are highly correlated without any time lag. We did not
observe any significant trend in color variation with time, but we observed a
bluer-when-brighter trend between the $B-I$ color index and the $R$-magnitude.
Optical $BV\!R$-band spectral energy distributions always show a convex shape.
Significant intraday variability was frequently seen in the quasi-simultaneous
observations of AO\,0235+164 made on 22 nights in $R$ and $V$-bands by the
CASLEO and CAHA telescopes during 1999--2019. We also estimated the central
supermassive black-hole mass of $7.9\times10^7 M_{\odot}$ by analyzing the
broad Mg II emission line in AO 0235+164's spectrum. We briefly explore the
probable physical scenarios responsible for the observed variability.
