Adamus Phillida is an imperial guard and was commander in the Imperial Legion but is now retired. He had apparently denied a request by Hieronymus Lex to put a bounty on the head of the Gray Fox who like most people he believes to be purely fictional.
He had been commander of the Imperial Legion in the city for 40 years and was the highest ranking member of the Legion in Cryrodill. Adamus had spent most of his career investigating and hindering the Dark Brotherhood in their operations. Adamus is one of the few people not intimidated by the Dark Brotherhood and willing to risk his life trying to put an end to them.
His retirement so annoyed the Dark Brotherhood who had three previously failed assassination attempts on Adamus and after his meddling in their affairs, interrupting contracts, and killing there 'family' members they couldn't allow him to peacefully retire. The Brotherhood's fourth attempted assassination on Adamus while he was at his most vulnerable was successful. To ensure no future problems with his successor they put the finger of Adamus with the Imperial Legion ring in his drawer as a warning. Unfortunately for the Dark Brotherhood his successor has vowed to continue Adamus Phillida's work and not cave in to their threats like so many other's have.
"Do you recall the name Adamus Phillida? The Imperial Legion pest? It's time he joined Sithis in the Void." -The Dark Brotherhood