The Christchurch-born and Massey University-educated Hillgrove, 47, came to work for the WikiLeaks figurehead after being connected by Assange's long-serving lawyer Jennifer Robinson, according to an interview with UK marketing and advertising trade news site, The Drum.
The Kiwi expatriate and founder of 6 Hillgrove Public Relations, who was convicted in 2014 on a £93,000 tax fraud, said he's trying to make Assange's PR "less personal".
"The cult of personality aspect around Julian Assange has caused a lot of his problems," Hillgrove told The Drum in a Q&A.
"It's, unfortunately, got very personal. It's almost as if people like former CIA director and now Secretary of State Mike Pompeo have got it in for Julian Assange on a personal level. Him saying, 'Julian Assange has no first amendment rights' is ridiculous.
"Even though he's broken no laws and simply published the truth, in exactly the same way the New York Times or Guardian do, they are treating him personally like some sort of criminal.
"The move [to] take him out of the editor role of WikiLeaks is a good start to de-personalising everything."
Hillgrove believes his PR skills have "greatly amplified" Assange's message but he wants to get "more supportive voices" come forward and to reinforce the United Nations ruling that he has been arbitrarily detained and that there are serious concerns about his health.
"Not just the usual voices like Vivienne Westwood and Pamela Anderson, but other people coming forward," Hillgrove said.
"Everyone's very frightened to put their head above the parapet."