What is the role of night Watchman in test Cricket?

Generally, in test matches at the end of day’s play, a tailender is sent for batting in the place of capable batsman. His role is to retain the strike till the close of play and thereby avoid the more capable batsman from getting out due to poor light or a phase of extreme tiredness.

Australian Player Jason Gillespie created history by scoring double century as a night watchman against Bangladesh in 2006.