(CNN) Donald Trump has finally hired someone he can't fire.
The presumptive Republican presidential nominee ended days of intense speculation and political drama on Friday, officially announcing via Twitter that he has chosen Indiana Gov. Mike Pence to be his vice presidential nominee -- a decision that pairs up two men whose personalities are day and night.
Famously brash and unfiltered, Trump has shocked the country throughout the election with his boisterous, and at times, colorful rhetoric. A former reality TV star, Trump's flair for showmanship has been evident at every turn of the campaign -- particularly this week, when he held a flurry of last-minute auditions with several VP contenders that sent the political media scrambling.
And now, the billionaire businessman is poised to head into the general election with a political partner who -- by all outward appearances -- appears to be his polar opposite.
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Pence is a devout evangelical 13 years Trump's junior, known to have a reserved and low-key public demeanor. Unlike Trump, the mild-mannered, Midwestern governor is hardly a natural attack dog, and the former radio show host appears far more comfortable sitting at a Sunday show roundtable than revving up a large crowd at a campaign rally.
"I saw him at the rally that he did with Trump and his attempt at passionate enthusiasm was Donald Trump's 'hello,' " said Brett O'Donnell, a GOP political veteran who has advised former GOP nominees John McCain and Mitt Romney.
And that contrast is not necessarily a bad thing, O'Donnell added: "It could be that they are complementary -- that Pence helps bring some discipline."
As Trump and his family deliberated over the VP finalists -- a small group that included Pence, New Jersey Gov. Chris Christie and former House Speaker Newt Gingrich -- a significant factor was whether Trump would ultimately feel comfortable with his eventual running mate.
Having known both Christie and Gingrich for years, it was Pence who emerged the biggest wild card.
Donald Trump selects Mike Pence as VP
To see if they meshed, Trump had dinner with Pence and his wife this week in Indiana. The next morning, Trump's family flew in from New York to spend time with the governor at his residence. If Trump worried that someone like Gingrich could overshadow him as his running mate, with Pence, he developed the opposite concern: that the first-term governor was boring.
Gingrich described the contrast this way during a Facebook live: "He had a choice between having two pirates on the ticket or having a pirate and a relatively stable, more normal person."
But Trump was under pressure from many of his closest advisers, including some of his children, to pick the Indiana governor. They argued that Pence was in many ways the safest pick: a deeply religious conservative widely respected by establishment Republicans and the right, he could help appease important constituencies and win over skeptics in the party.
And his low-maintenance style meant he was unlikely to go off-script and embarrass Trump.
Lanhee Chen, who advised Romney in 2012, said it was clear that in the Trump-Pence partnership, there would only be one boss.
"Trump is very much going to be a guy who will be in charge and he is going to call the shots," Chen said. "What will be interesting if Pence can play the attack dog role -- and maybe the answer is, you don't really need that because Trump himself is such an aggressive attacker."
But even after word spread that Trump had chosen Pence, he appeared to have nagging reservations. Late Thursday night, Trump asked top advisers if he could pull out of his decisions, and was told he could not, sources told CNN's Dana Bash.
Ultimately, Trump's decision to go with Pence was at least a partial concession to those in his inner circle -- choosing someone that would help balance him out, both in terms of temperament and skills.
Pence is expected to be a relatively steady hand next to Trump's volatile style, and bring to the ticket a wealth of knowledge about the workings of Capitol Hill and Washington.
"As Trump himself has stated, 'chemistry' is very important, but that can mean different things. It's more than just getting along or liking each other," said former Minnesota governor and presidential candidate Tim Pawlenty. "For example, different skills or styles can blend to help avoid blind spots that might have otherwise been missed. That can be real chemistry."