Excessive coming in to fake name no longer known (9)
I believe the answer is:
forgotten
'no longer known' is the definition.
(I've seen this before)
'excessive coming in to fake name' is the wordplay.
'excessive' becomes 'OTT' (short for 'over the top').
'coming in to' is an insertion indicator.
'fake' becomes 'forge' (synonyms).
'name' becomes 'n' (common abbreviation e.g. on forms).
'ott' inserted within 'forge' is 'forgotte'.
'forgotte'+'n'='FORGOTTEN'
(Other definitions for forgotten that I've seen before include "Overlooked" , "Not accessible to memory" , "Ignored" , "Unremembered" , "Gone from memory" .)