Why did Harry Carpenter call Ali his slave name Cassius Clay?

[Bill Paxtom]

When you look at him,

You just know he's a Cassius.

When he opened up those 'rotten' fast food joints 'Champburgers', there
wasn't one thing on the Menu called 'Muhammad' or 'Ali'.

He did have 'Cassius Clay's Chicken Bucket' though.

Seems that old Cassius was a 'businessman' first, and Muhammad Ali second.