King follows his noble, barking Great Dane (5,4)
I believe the answer is:
niels bohr
'great dane' is the definition.
(Danish physicist)
'king follows his noble barking' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'follows' says to put letters next to each other.
'barking' is an anagram indicator (UK slang for mad).
'his'+'noble'='hisnoble'
'hisnoble' is an anagram of 'nielsboh'.
'r' put after 'nielsboh' is 'NIELS BOHR'.
(Other definitions for niels bohr that I've seen before include "14 [GREAT DANE]" , "Danish physicist" , "Atomic scientist" .)