Since retirement, tennis legend Steffi Graf has maintained a fairly private life after being one of the biggest stars of the tennis world. SI's Jon Wertheim shares his thoughts on Graf and her interesting legacy.

Robin Lundberg: Happy birthday to Steffi Graf, the former tennis star celebrated over the weekend. For more, I'm joined by our senior writer, Jon Wertheim. Jon, what's the status with Steffi Graf right now? She just turned 51.

Steffi Graf: It's a great question. And it got a lot of chatter on Twitter. This is what we do, Robin, when there are no live matches, we talk birthdays. But that's Steffi Graf is absolutely towering figure in tennis history. She, of course, married Andre Agassi. They live in Las Vegas. But she is really divorced herself from tennis. A lot of people have tried to be in touch with her. Maybe she'd like to come to a ceremony. Maybe she'd like to do an interview. Maybe she'd like to coach. She's really kept a low profile. And she said she would when she left the sport 20 years ago. And to me, it's interesting how that has sort of impacted history that I think get a little bit. She's been lost in the shuffle of Chris Evert is on ESPN and it's very much out there and does a lot for the sport. Martina Navratilova is on Tennis Channel. She's a very public figure. Billie Jean King, same thing. I think in tennis, perhaps more than other sport when players leave the public arena, I think that in some ways affects their image a bit. But I think we talked about it last week. John McEnroe has this huge image. And yet people don't always realize, you know, there are a lot of players that won more majors and had more accomplished career. So Steffi Graf turns 51, it gave us a chance to put it on social media for people to revisit her contributions. And I think because she is such a private figure in the last 20 years into retirement, maybe she doesn't get her full due.