Cox announced on Monday that he would retire at season's end. The 32-year-old's decorated 15-year career includes a premiership, a best and fairest and six All Australians.
Simpson said Cox is one of the most "unique" ruckmen to have ever played.
"He's a champion of the game," Simpson said.
"He's just so unique because he's adapted with the game and not many ruckman can say they've done that.
"You quite often get drafted with a strength and that's your strength for your whole career and I think what Dean's done is his ability to adapt to the competition, and that's what's given him six All Australians and that's why he's held in such high regard."
Simpson's insight into Cox is acute, having played against him as an opposition midfielder during his career with North Melbourne as well as having coached against him as a midfield coach at Hawthorn before joining West Coast.
"It's really hard to prepare for opposition players when their footy smarts are their main asset," Simpson said.
"You can't stop that. His footy smarts are what I thought got him a 15-year career."
In his first year as West Coast coach Simpson observed that Cox was the life-blood of the club and although he will be huge loss as a player he believes he will be an enormous gain as a coach.
"I've seen what he does around the club more than anything," Simpson said.
"He's the heartbeat. I just spoke to the players about that as well. He will be sorely missed in that area. But we gain him as a coach next year."
Cox has been working as the Eagles' ruck coach this year and Simpson said he has a bright future, not just as a specialist coach.
"I think there's a future, a long future in Dean's coaching apprenticeship," Simpson said.
"His footy smarts have come through in his coaching as well."
Cox said he's looking forward to step into a full-time coaching role.
"I love it," Cox said.
"I've really enjoyed this season and being able to get a taste of what's required to understand players, to pass on knowledge, to understand how players learn best.
"It's an avenue I want to pursue as soon as I finish. So in six weeks time, hopefully we play finals and it's longer.
"But as soon as the season finishes, I'm really looking forward to the next chapter."
