The selection of HIV/AIDS activist Jeff Sheehy as the city’s newest supervisor will make life more interesting — and volatile — at City Hall.

Mayor Ed Lee announced his pick Friday morning after weeks of considering candidates to fill the vacancy left by Scott Wiener in District Eight, which includes the Castro, Noe Valley and Glen Park, when Wiener was elected to the state Senate in November.

That Lee went with Sheehy, 59, indicated he is willing to ratchet up tensions at City Hall to move his goals forward and make sure progressive Supervisors Aaron Peskin and Jane Kim don’t dictate the agenda. But his choice also carries the risk that the independent-minded Sheehy won’t always fall in line.

“He’s wicked smart and a total bully if he doesn’t get his way,” said one city employee who worked with Sheehy and asked to remain unnamed because they may work together again.

On Friday, at a news conference in Noe Valley to announce Sheehy’s appointment, the mayor described him as a “forward-thinking, solution-oriented, pragmatic, practical, yet value-spirited person.”

In personality, Sheehy stands in vivid contrast to the mild-mannered Lee. And while Lee is a moderate, Sheehy has historically positioned himself as a progressive. Sheehy emerged as the leading candidate in large part because of his bulldog personality and independent streak, sources close to the decision said.

Sheehy’s politics have also shifted toward the moderate, and the mayor reportedly wanted someone who could go toe-to-toe with the progressives and wouldn’t feel threatened by aggressive tactics.

Amanda Fried, the city treasurer’s legislative manager who worked with Sheehy when she was an aide at the Board of Supervisors, called him “a fighter before other people were on board” when it came to issues affecting the gay community.

“He was impatient in the best way,” she said.

Sheehy could serve as supervisor for as long as 10 years — two years filling out the rest of Wiener’s term plus two full terms. He is not scheduled to run for office until 2018, but there is a real possibility progressive supervisors could force a special election this year.

Rafael Mandelman, a member of the City College of San Francisco Board of Trustees, is the leading candidate to take on Sheehy. If there is a special election, Sheehy would have to run to fill out the rest of Wiener’s term.

On Friday, Mandelman said he is “seriously looking” at running and will make a decision this year.

The appointment of Sheehy generated immediate praise — he will be the first openly HIV-positive person to serve on the board — and criticism.

“It was a very shrewd choice on the part of the mayor. It was good on the substance and good on the politics,” said former Mayor and Lt. Gov. Gavin Newsom. Sheehy was Newsom’s HIV/AIDS adviser.

“He is not timid ... he has got grit. He doesn’t suffer fools, and he has a record of accomplishment,” Newsom said.

But outgoing progressive Supervisor David Campos, who, like Sheehy, is gay, criticized the appointment.

“Thank you Mr. Mayor! Such a divisive choice is a big plus for progressives,” Campos tweeted. In a follow-up tweet, he wrote of Sheehy: “His political toxicity has nothing to do with HIV status but rather his divisive approach to politics.”

Campos accused Sheehy, the longtime director of communications for the UCSF AIDS Research Institute, of being behind a story last year suggesting that he and Kim wanted to cut funding for the Getting to Zero initiative to reduce new HIV/AIDS cases.

“He has had the reputation of being someone who hits below the belt and takes it too far,” said Campos — who has his own reputation for being truculent.

Sheehy has been especially critical of Kim. He told the Bay Area Reporter in June that Kim “doesn’t seem to understand what’s going on with people who have HIV and AIDS.”

And in the lead-up to the state Senate race between Kim and Wiener, Sheehy dismissed Kim as having a “lackluster” record on lesbian, gay, bisexual and transgender issues.

On Friday, Kim downplayed the attacks.

“I really don’t know Jeff. I don’t think we have ever met each other,” she said. “When you are done with campaigns, whether you are the candidate or not, everyone has to come back into the room and work together. And for me, that’s how I am going to approach the newest member of the Board of Supervisors.”

Peskin said his immediate response to Sheehy’s appointment was, “Hmmm, that’s kind of interesting.”

“He has always struck me as independent, which I think voters like,” Peskin said. “He has always been his own guy — which, in terms of mayoral loyalty, which everyone seems to think is the mayor’s No. 1 consideration, may be a little more problematic than they envision.”

Far from being threatened by criticism, Sheehy has ridiculed critics and people he disagreed with.

As AIDS czar to Newsom, he colorfully lambasted a city official who wanted to reclassify erectile dysfunction medicines as controlled substances.

“Jeff Klausner wants the dicks of people with HIV in his back pocket, and he wants us to ask him permission to use it,” Sheehy told the Bay Area Reporter. “And I am not going to give him my dick.”

Sheehy’s early dive into local politics came in the 1990s and early 2000s. He was president of the progressive-leaning Harvey Milk LGBT Democratic Club and served on the San Francisco Democratic County Central Committee.

He was an influential proponent of the landmark Equal Benefits Ordinance, which required companies doing business with San Francisco to provide the same benefits to domestic partners as they did to married couples.

But many of the issues he fought for — greater protections for LGBT couples, same-sex marriage, more treatment for people with HIV/AIDS — have become widely supported in San Francisco.

Today’s divisive issues of the day revolve around housing, how much to restrict short-term rentals and how to deal with the homeless crisis.

In the end, moderates, including Wiener and some of the mayor’s top advisers, encouraged Lee to appoint Sheehy, believing that he would be a strong supervisor, formidable candidate and, for the most part, an ally.

At the news conference Friday announcing his appointment, Sheehy emphasized his family values, commitment to neighborhood and desire to work with his colleagues. He said he never expected to live this long — he was diagnosed in 1997 — much less become a supervisor.

“I literally would not be here if City Hall had not come together” to fight the HIV/AIDS epidemic, he said.

“I want to again make a plea that we act without rancor, we disagree civilly and we keep our eye on the ball so that we can defend ourselves against threats that are real to everybody in this community.”

Whether that comity comes about or how long it lasts is anyone’s guess.

Emily Green is a San Francisco Chronicle staff writer. Email: egreen@sfchronicle.com Twitter: @emilytgreen