Here I have combined all information I have got about him so far through searching online:

Atul Kapoor, the unassuming guy in his mid-40s, likes to be low-profile but his voice is enough to create awe and respect in the hearts of people. Remember Bigg Boss 4 contestant Veena Malik who said that she has a huge crush on Bigg Boss. Well, you can see her hanging around with hm. Atul Kapoor has also had his photos taken along with other Bigg Boss contestants from the past, the likes of Ashmit Patel, Urvashi Dholakia and many more.
Kapoor, we hear, has been a regular on radio, and it was his commanding baritone that made him the perfect choice for Bigg Boss. "His deep, husky voice makes him return with each season.
And he is being paid handsomely for it," the source adds. Like the housemates who are kept in seclusion, away from all human contact other than with their co-residents, Kapoor too is housed in a separate room in the House which has been set up in Karjat, a two-hour drive away from Mumbai.