Let's start at the very beginning- H.O.T versus Sechskies. Back in the late 1990's, H.O.T, considered to be the first true idol group, battled things out against Sechskies. Each group had its devoted fanbase, which introduced fan culture to K-Pop. Since then, fans haven't backed down from their fervent love of idols. Both groups have too many amazing songs to focus on the competition in depth, but many newer fans got to witness the legendary rivalry in the drama Answer Me 1997.

Other idol rivalries followed, but none quite as large as TVXQ versus SS501. The two five-member idol groups battled it out starting in 2005 when SS501 debuted (two years after TVXQ.) The groups had two of the most popular fanclubs in Korea prior to the latest kings of idols, and both groups are still immensly popular. Based on their flower-boy appeal and beautiful vocals, TVXQ and SS501 were and still are often compared to one another.

While TVXQ's affect on K-Pop may be more tangible (because it still is active, even if split into TVXQ and JYJ,) SS501's fanclub is still very prominent in Korea, and fans still are anticipating the day that the group will reunite.

The next rivalry is still ongoing- Big Bang versus Super Junior. Even though the groups are fundamentally different in size and musical style, the fact that "Lies" and "Sorry Sorry" both became hits within months of one another has led to an ongoing competition. Even though Super Junior's ELFs and Big Bang's V.I.Ps are constantly at odds with one another, the two groups have a fairly friendly relationship.

Then there's the rivalry of rivalries- BEAST versus MBLAQ. Debuting around the same time, MBLAQ and BEAST were up against one another since their very first songs. While MBLAQ was originally hailed as "Rain's Group" and BEAST as "The Reject Group," each group went on to do extraordinarily well. Even though they were put up against one another from the start, BEAST's and MBLAQ's members have shown that they're very close in the past, making fans give them the nickname "MBLEAST."

Rounding out this list is the latest rivalry, between EXO and B.A.P. Debuting with similar "planet" concepts, where the members are supposedly from outer space, fans immediately began to draw parallels between the two groups. Their different styles attract different fans, but B.A.P's held it's own even while EXO's fanclub is a force to be reckoned with. The groups have shown affection towards one another, despite their rivalry.

Honorable mention: FT Island and CNBlue were going to be included on this list, but as they are from the same company, they're not exactly rivals but have a senior-junior relationship.