What is his breeding? You could incorporate part of his breeding into his name. My favorite Shakespere play is Othello, but it's been used a lot probably. You might think Othello and add part of his registered name. I'll think some more.
After I clicked off, I noticed a thread of "Black actors who ride" or something like that in "Off course". You could cruise the thread for ideas. For example I love everything Samuel L. Jackson does, I would be inclined to name him something that had to do with his movies and call him Sam for short. "Satchmo" is good, but alas it is also probably been overused.
RIP Kelly 1977-2007 "Wither thou goest, so shall I"
"To tilt when you should withdraw is Knightly too."
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Is the registered name so awful that you can't use it? (I have a couple with really bad names, so I can understand why you'd want a change). It's when horses get name changes that their breeding gets lost. When the breeding gets lost, it's hard to trace down good ancestors that are productive for current performance horse.
How about Incubus, for a name if you do want a change.
"I'm a lumberjack, and I'm okay." Thread killer Extraordinaire