Silver Star

A purple unicorn named Silver Star, yes. So what? X3 ...His eyes are silver. That counts as far as I'm concerned.

Anyway, I'm aware the whole 'Dinky's father' theory has been done to death, but here's my take on it anyway.
This is Silver Star, a show colt and Derpy's childhood friend eventually turned first boyfriend.
A few days after asking Derpy to marry him, Silver attended a fashion show after-party, but suffered a severe anaphylactic reaction from some of the food, and had to be hospitalized.
Derpy was devastated when she learned Silver wouldn't be able to pull through, and some of her last words to him were that she was pregnant with his foal.
Before he passed, Silver told Derpy to never forget him, that he was sorry that he couldn't marry her like he promised, and to take good care of the foal after it was born.
A few days later, at Silver's funeral, Dr Whooves met Derpy, and after realizing her situation, told her that if she needed somepony to talk to, he would always lend an ear. Eventually, the two of them slowly grew closer, formed a relationship, and a few months after Dinky was born, married and settled down together.

To this day, Derpy and Dr Whooves visit Silver's gravestone to say a prayer she dedicated to him, and put flowers on it.