Seung Hyun Choi performed a song, titled "Hallelujah," along with his fellow BIGBANG group members G-Dragon (Ji-Yong Kwon) and Taeyang (Young-bae Dong), for this series.
Tae-hee Kim played the female lead character for the show's first season and Da-hae Lee played the female lead character for the second. Kim is married to singer Rain and Lee is married to singer Se7en at the time. Rain (from Korean music company JYP Entertainment) and Se7en (from Korean music company YG Entertainment) were solo singer rivals from two rival music companies, JYP Entertainment and YG Entertainment.
Actor Min-jong Kim was originally supposed to reprise his role as Kim Ki-soo (from Athena: Goddess of War (2010-2011) for the second season of Iris (2009). However, his popularity for his most recent show, A Gentleman's Dignity (2012), was still too fresh and fans were not ready to see him return as the North Korean escapee. Ki-soo's part in the script was changed to a new character, named Yoo Joong-won. The part went to Beom-su Lee.
Two scripts were written for the second season: one where the original cast returns and another with a new cast and most of the original cast members making cameo appearances. Byung-hun Lee and Tae-hee Kim's schedules were too busy for them to return, so the filmmakers had to go with the latter.
There is a deleted clip of Jin Sa-woo, played by Joon-ho Jung, blending in with the crowd during the boxing match in Cambodia, with Beom-su Lee's character in the first episode of the second season. For unknown reasons, the clip was cut out of the show.