Since I retired, I very much enjoy watching Serena Williams play. While I was playing, she was one of the toughest players I ever faced. Her ground strokes are so solid, her serve is one of the most powerful in women's tennis, and mentally she is just so strong.

For me, the biggest thing with money has always been independence - just the biggest.

I lost my dad way too early and it was agonisingly awful. I missed him so much and I hated knowing that I could never again pick up the phone to tell him about my day.

That's the key to success, isn't it? It has to be fun.