Theme songs of popular TV dramas are usually very much loved by the viewers. SBS TV’s drama “All In” starring actor Lee Byung-heon and actress Song Hye-gyo is enjoying its popularity and so is singer WHO who sang that theme song “Like the First Day.” The original soundtrack of the drama “All In” was released in late January and people are wondering just who WHO is for he hasn’t made any media appearance. “Like the First Day” is currently people’s number one choice for caller ring service.