Regularly save genial criminal influencer (8)
I believe the answer is:
svengali
'influencer' is the definition.
(thesaurus)
'regularly save genial criminal' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'criminal' is an anagram indicator.
The alternating letters of 'save' are 'sv'.
'genial' with letters rearranged gives 'engali'.
'sv'+'engali'='SVENGALI'
(Other definitions for svengali that I've seen before include "One exerting evil mental control over another" , "evil manipulator" , "George du Maurier character who controls Trilby" , "George du Maurier's controlling character" , "Person who controls another's mind - musician and evil genius (created by George du Maurier)" .)