Princess Gwenevere and the Jewel Riders
I just barely remember when this cartoon was on... the theme song more than anything is what triggered my memory. Although I never watched this as a teenager, or had any of the toys, I really think this was a great line of figures in it's day.
The toyline had 3 series, but only one figure was released in the third one. Two horses were produced as well. They certainly could have done more with this toyline, but I'm guessing it lost steam, and they couldn't do more.
This toyline and cartoon came out in the mid-90's, and to be honest, I don't know which came first. There were 3 main characters, Gwenevere (Starla) being the main one. The first few episodes take us through her journey to becoming a Jewel Rider -- that means she is granted special powers to help protect the jewels of the kingdom of Avalon from her evil aunt Lady Kale.
These characters came out in the UK as Starla and the Jewel Riders. Again, I'm not sure if it originated there, or why the name change. The figures were exactly the same, but with packaging differences.