Ruler’s team appear dour regularly (7)
I believe the answer is:
emperor
'ruler's' is the definition.
(I've seen this before)
'team appear dour regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'team'+'appear'+'dour'='teamappeardour'
The alternating letters of 'teamappeardour' are 'EMPEROR'.
(Other definitions for emperor that I've seen before include "Ruler - penguin - size of paper" , "Beethoven's Piano Concerto No. 5 in E-flat major" , "noted by Beethoven" , "Male ruler of a group of countries" , "He rules over several states" .)