While Generation 2 didn't have movies or shows it was when Hasbro first worked with the idea of main characters in the toy line. There were main characters in the G1 shows and movies, but this was not reflected in the toys the way it has in all following Generations. The My Little Pony Tales main character toys weren't even sold in North America.
G2's main character was Sundance, followed (in no particular order) by Sweet Berry, Ivy, and Light Heart. Each of these characters were re-released many many times, in the same way the Core 7 was in G3 and the Mane 6 is in G4.
The main role of these characters was stressed as they were almost exclusively the only ponies featured on G2 Merchandise.