How long has SBD been around?

I'm curious to know, how long has SBD, or Steem Backed Dollars, actually been in existence? I've been hearing a lot about it lately and I'm wondering if it's a recent development or if it's been around for quite some time. Understanding its history and longevity could give me a better idea of its stability and potential for growth in the future. So, if you don't mind, could you provide me with a brief overview of SBD's timeline and how long it's been operational?