You know them as the weird unexplained toys, Princess Sterling (packaged with Fluttershy) and Princess Golden Lily (packaged with Pinkie Pie)

I decided to redesign them for my headcanon as the mothers of Celestia and Luna. In their time the Elements of Harmony didn't have specific names, it was more so "this specific group of ponies can activate these magical artifacts" and the names evolved overtime (healing to kindness and hope to laughter, etc.)

For some context, Equestria wasn't all that plain and underwhelming when Grogar declared himself emperor but his constant streams of monsters with powerful dark magic beyond their understanding meant the ponies and some kingdoms around them were whittled down nearly back to square one. Aside from the efforts of many heroes all memory and record of the Queens and the original elements were lost.

Sterling Rainbow

Sterling was an incredibly understanding and often a too forgiving pony, this helped her as a queen not just with her own citizens but with others too. Under her relationships between the species were never better than they would be again until Twilight Sparkle. Although this wasn't as difficult a feat as the area beyond Equestria hadn't been explored yet to their true extent. She prided herself on being able to truly look into the heart of a creature and help them even if she didn't truly understand but she could be a bit naive at times. Sterling hoped that every pony would act out of true pure intention so she acted as though they did. She could be a bit of a nerd sometimes, especially when it came to weather and color magic. Sterling firmly believed magic could be harnessed by all creatures and if magic study wasn't in such an early stage at the time she would have funded the technology to aid those who couldn't to do so.

After her death she was buried by the other elements and her magic and body fertilized the ground that would eventually become the Tree of Harmony. The spirit that comes from the tree in the form of Princess Twilight to speak to the student six is actually her soul.

Golden Darkness

Golden was a source of endless positivity but not an overwhelming one, she was definitely more realistic and understood there were things out of their grasp to help with at their time. She was the one who went outside and interacted, making the public appearances and such. Ponies in this day weren't nearly as prudish. Especially about death and magic surrounding it. Golden Darkness actually attended many funerals herself and gave her blessing, not just to royalty but to the common folk who she knew might need extra support and resources after losing one of their own. With her close relationship to the Alicorn of life Goldy understood that life is a cycle and she didn't want her subjects to spend their magical resources and their lives in search of staving it off. A view also inspired by Sterling she believed harmony wasn't just for ponies; the earth, sea, and sky played just as big a part. The biggest lesson she sought to teach her subjects was that one day everypony would return to them and that was nothing to be afraid of.

Ironically, she would not move onto the afterlife herself, she is now somewhat still present as the spirit that guides ponies into the afterlife.

Bases by starryoak and elementbases