These were the most impactful and cannot be forgotten for me ~
1. From first generation of KPOP's "father" group, the male trio group known as Seo Taiji & Boys with their debut song called "I Know."
His group opened doors for future artists.
This is for KPS members who probably also grew up during that era and were aware of the group's existence.
To those who do not know, Yang HyunSeok [ the tallest one in the I Know MV wearing the black shirt ] was a member of this group and created his label YG Entertainment, hence the reason for the influence in debuting hip-hop music style artists like Big Bang, 2NE1, and so on.
2. From second generation of KPOP girl group, Girls' Generation's Gee.
They really made their era a "Girls' Generation" because although there were other groups prior to them, they were coined affectionately as, "The Nation's Girl Group GG." in South Korea.
There were many labels who debuted their rookie groups afterwards and tried to emulate/copy GG because the trend of the age-appropriate cutesy, innocent vibes in music style was what appealed to the masses.
I believe a lot of those other groups had found massive success as well.