Ancient royal on a slide messed about (8)

I believe the answer is:

leonidas

I'm a little stuck... Click here to teach me more about this clue!

'ancient royal' is the definition.
The definition suggests a singular noun which matches the answer.

'on a slide messed about' is the wordplay.
'messed about' indicates anagramming the letters.
'on'+'a'+'slide'='onaslide'
'onaslide' is an anagram of 'LEONIDAS'.

Can you help me to learn more?

(Other definitions for leonidas that I've seen before include "Spartan king killed at Thermopylae" , "Sailed on (anag) - Spartan king" .)

I've seen this clue in The Sunday Times.

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