  Giant radio galaxies (GRGs) are one of the largest astrophysical sources in
the Universe with an overall projected linear size of ~0.7 Mpc or more. Last
six decades of radio astronomy research has led to the detection of thousands
of radio galaxies. But only ~ 300 of them can be classified as GRGs. The
reasons behind their large size and rarity are unknown. We carried out a
systematic search for these radio giants and found a large sample of GRGs. In
this paper, we report the discovery of 25 GRGs from NVSS, in the redshift range
(z) ~ 0.07 to 0.67. Their physical sizes range from ~0.8 Mpc to ~4 Mpc. Eight
of these GRGs have sizes greater than 2Mpc which is a rarity. In this paper,
for the first time, we investigate the mid-IR properties of the optical hosts
of the GRGs and classify them securely into various AGN types using the WISE
mid-IR colours. Using radio and IR data, four of the hosts of GRGs were
observed to be radio loud quasars that extend up to 2 Mpc in radio size. These
GRGs missed detection in earlier searches possibly because of their highly
diffuse nature, low surface brightness and lack of optical data. The new GRGs
are a significant addition to the existing sample that will contribute to
better understanding of the physical properties of radio giants.
