  India's largest size 3.6 meter Devashal optical telescope (DOT) was
commissioned in the year 2016, though the idea of building it germinated way
back in the year 1976. This article provides research accounts as well as
glimpses of its nearly four decades of journey. After a decade of site surveys,
location of Devasthal in central Himalyan region of Kumaon was identified.
Thereafter, a detailed site characterization was conducted and project
approvals were obtained. The telescope is designed to be a technologically
advanced optical astronomy instrument. It has been demonstrated to resolve a
binary star having angular separation of 0.4 arc-sec. After the technical
activation of the telescope on March 30, 2016, it has been in regular use for
testing various back-end instruments as well as for optical and near-infrared
observations of celestial objects. Back-end instruments used for these
observations are 4KX4K CCD imager, Faint object imager cum spectrograph and
TIFR near-infrared camera-II. A few published science results based on the
observations taken with the telescope are also presented. Furthermore, the
routine observations find that for a good fraction of observing time the
telescope provides sky images of sub-arc-second resolution at optical and
near-infrared wavelengths. This indicates that the extreme care taken in the
design and construction of the telescope dome building has been rewarding since
the as-built thermal mass contributes minimally so as not to degrade the
natural atmospheric seeing measured at Devasthal about two decades ago during
1997-1999 using differential image motion monitor. The overall on-site
performance of the telescope is found to be excellent and at par with the
performance of other similar telescopes located over the globe.
