The Real Madrid goalkeeper and current Spanish boss believe modern sport has lost once of its key figures after the death of the former Atletico Madrid man on Sunday
Aragones, who led Spain to Euro 2008 glory, passed away after illness in Madrid in the early hours of Saturday.
Casillas, who played under Aragones throughout his four-year spell at the helm of la Roja, says football should be grateful for the impact of the former Atletico Madrid player.
"He has been one of the most influential people for me. Football should be more grateful. His ideas have brought great success to this day. He'll always be remembered," Casillas is quoted as saying by Sefutbol.com.
"I owe him a lot personally. He has influenced me greatly since I was 26. I've always had a lot of affection for him and I know it was mutual.
"I want to send my condolences to his family. He will always hold a special place in the history of our football. It's a sad day for Spanish football."
Del Bosque, who succeeded Aragones as Spain coach in 2008, believes the former Barcelona boss was a pivotal figure in paving the way for Spain's period of dominance of international football.
"We will remember this day with great sadness," he said.
"Without a doubt, he led the way in this most recent era of success. He had a long experience as a coach and, personally, I had a special appreciation for him.
"We have lost a key figure in modern sport."