DETROIT – The world is mourning the death of Muhammad Ali, whose greatness as a boxer transcended the sporting world. Members of the Verizon IndyCar Series paddock have paid their respects this weekend as well.

A number of drivers and others have taken to Twitter this weekend to acknowledge Ali, the self-proclaimed “greatest of all time” who was a guest at the Indianapolis 500 in 2003.

The following are a few tweets to honor Ali:

#RIPMuhammadAli, possibly the greatest athlete this world has ever know, and a social figure larger than life. #GOAT

— Graham Rahal (@GrahamRahal) June 4, 2016

RIP Muhammad Ali! A true champion! Simply the greatest!

— Stefan Wilson (@stef_wilson) June 4, 2016

Amen. https://t.co/xPh8R3SsaM

— Mario Andretti (@MarioAndretti) June 4, 2016

RIP Muhammad Ali...#TheChamp #legend pic.twitter.com/h4IsSyuPwU

— Carlos Munoz (@CarlosMunoz034) June 4, 2016

Such a legend. RIP @MuhammadAli 🙏🏼🙏🏼 #flyhigh pic.twitter.com/0jMOHRlWtO

— Sage Karam (@SageKaram) June 4, 2016