The 'Mrs Doubtfire' star committed suicide in August 2014 but had been battling Lewy Body Dementia prior to his death and Susan hopes his passing will provide a "legacy" to help other dementia sufferers.
Speaking in the upcoming special 'People Icons: Gone Too Soon,' she said: "Robin's real legacy will unfold in the decades to come and really shed light on brain disease as a whole, but particularly dementia, which 47 million people worldwide are suffering right now.
"And for [other Lewy Body Dementia patients] to know that they are not alone, that this is what Robin Williams had and they're being heard, they're not outcasts. So the way I see it, he truly is on that back nine going, 'I got this,' where he made people feel not alone before. They don't have to feel alone now."
And Susan remembered her "quiet and intellectual" husband, who she dubbed an "observational genius".
She added: "The Robin that I knew was not the crazy, manic one who would be performing on stage for comedy or sometimes in his roles as an actor. And I think that's commonly a misconception, is that Robin was always running at that speed. And that is not the man that I knew. That's not the man I fell in love with.
"Robin was a quiet, intellectual man, sometimes playful. But primarily what moved him was the fact that he was an observational genius. And if you can imagine the energy that he would bring to the stage - no one can do that full-time. And I think the brilliance behind that impact of energy he would bring was because, in his time off, he was someone who was contemplative and an observational genius."