Retired astronaut Mark Kelly has announced he will run to finish John McCain's last term in the US Senate.
If he wins the Democratic nomination, Mr Kelly would take on Republican Martha McSally in what is expected to be one of the most closely contested Senate races of the 2020 elections.
Mr Kelly has billed himself as an independent-minded centrist who will take a data-driven approach to solving problems such as climate change, wage stagnation and health care affordability.
The 2020 election will decide who finishes the last two years of Mr McCain's term, with the winner having to run again for a full six-year term in 2022.
So, if 54-year-old Mr Kelly is nominated, what can Arizonans expect to see from him?
Gun control
He became a prominent advocate of gun control after his wife, former US Congresswoman Gabrielle Giffords, was caught up in a mass shooting in January 2011.
Ms Giffords was severely wounded at a meet-and-greet event in Tucson. Six people were killed and she was one of 13 injured.
The pair have since pushed Congress to enact gun control measures - but with little success.
They shifted their focus to state legislatures in recent years, helping to strengthen background checks and domestic violence protections.
Joint campaigning with his wife
Ms Giffords played a prominent role in the four-minute video launching Mr Kelly's campaign.
"I thought then that I had the risky job," Mr Kelly said to Ms Giffords. “Turned out, you were the one that had the risky job."
Mr Kelly said Ms Giffords, who had been a rising Democratic star before the shooting, will join him frequently during campaign appearances.
Independent thinking
Mr Kelly, who flew four space missions over 10 years and commanded the Space Shuttle Endeavour in 2011, said: "You see a lot of partisanship in Washington and a lot of polarisation, and to some extent we've created that.
"It's going to take people who are more independent to fix it.
"Arizonans value independence."
More experienced opponent
Mr Kelly has never held elected office. If nominated, he will oppose Ms McSally, a former Congresswoman and trailblazing Air Force pilot.
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She was appointed to Mr McCain's seat after narrowly losing to Democrat Kyrsten Sinema in November last year for the other Arizona seat. This had been vacated by outgoing Republican Jeff Flake.
Ms McSally leaned heavily on her record as the first woman to fly a combat mission, but she was hurt by her embrace of president Donald Trump.
Impact on Democrats
Democrats are eagerly watching the Arizona contest, having already defeated Ms McSally.
The party is also gauging whether Arizona could be competitive at presidential level in 2020.
Mr Trump won the state in the 2016 presidential elections.
Additional reporting by Associated Press.
