Before he first came to fame as the winner of "The Ultimate Fighter" Season 17 middleweight tournament in 2013, Kelvin Gastelum worked as a bounty hunter in Arizona.

Armed with hand guns and wearing a bullet-proof vest, Gastelum often entered the homes of dangerous criminals as he set out on a single-minded goal to bring them to justice for the prize at hand. Despite the inherent danger of the job, it was never personal, it was just business.

"It got the heart pumping a little bit and the adrenaline pumping through the body a little bit because you don't know what to expect," Gastelum told CBS Sports on Tuesday.

One could make the comparison that Gastelum (15-3, 1 NC) will make a somewhat comparable hunt to his old profession when he challenges middleweight champion Robert Whittaker (20-4) on Saturday, in his backyard of Australia, in the main event of UFC 234 in Melbourne.

"[Bounty hunting] was life threatening and what we do now [in UFC] is life threatening, too, but it's a different kind of challenge," Gastelum said.

"I don't dislike Rob. I think he's a great guy; he's a family man by the looks of it. He's a hard worker. This is nothing personal towards Rob, this is all business. The only thing that makes it personal is that he has what I want, which is that belt."

Despite entering at the peak of his physical prime at 27, Gastelum's journey from TUF champion to his first UFC title shot has been anything but a straight line. Five years, three defeats, one failed drug test (for marijuana metabolites) and a failed experiment at welterweight later, Gastelum enters as the decided underdog with many questioning whether his resume is deserving of the opportunity.

"I think people have a misconception of me because of my past," Gastelum said. "From missing weight, people think I'm undisciplined. I don't look as chiseled and as muscular as the other fighters. I feel that's why people write me off and that's OK with me. I'm not in here to be a model, I'm here to fight and win fights and be world champion.

"My life has been pretty public since I won 'The Ultimate Fighter,' my lows and my highs. I just feel like those setbacks have molded me into the person I am now and I feel like now is the time that I'm mature enough to be able to handle these things. I'm mature enough to be able to make the right decisions. Now is the time."

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Being the underdog is something Gastelum embraces because, as he often mentions publicly, he has been there before. Nothing he has accomplished as a fighter has come easy or been given to him.

Gastelum has also read the stories of those who are writing him off as simply a rebound opponent for Whittaker, who returns for the first time in eight months due to hand surgery following split-decision win over Yoel Romero in their all-action rematch. He's also well aware of the best-laid plans for the promotion following Saturday's card.

Israel Adesanya, a native of Nigeria who fights out of New Zealand, has all the makings to be a crossover star in waiting for UFC. Should he get past legendary former champion Anderson Silva in Saturday's co-main event, an all-Oceanic showdown for control of the middleweight division's future between Whittaker and Adesanya sits high up on the short list of best fights that can be made in the sport.

"I'm sure everybody would like to see that," Gastelum said. "I'm sure UFC would promote that pretty greatly. So, yeah, I see myself as somebody who ruins plans.

"I don't see myself as a heel, I just think [the crowd] will be cheering for their countryman. I'm coming in to ruin [Whittaker's] plans. I'm coming into this country and I'm going to ruin his plans."

Gastelum coached opposite the 28-year-old Whittaker last fall during Season 28 of TUF. Although their interactions together were limited, Gastelum said he could feel an underlying tension between them. He could also see how much Whittaker was a competitor and hated losing.

But whether it's the burden placed upon Whittaker of headlining a pay-per-view card in his home country or the constant whispers of just how good a fight against Adesanya would be, Gastelum believes the pressure entering UFC 234 is entirely on the shoulders of the reigning champion. Even though critics and oddsmakers have been quick to give the nod to Whittaker when handicapping this fight, Gastelum thinks it will ultimately come down to intangibles.

"Once you get in the cage with me, you feel it. You feel how fast I am, you feel my hands and how hard they hit. You feel my wrestling and how strong I can grab," Gastelum said. "It's just little intangibles that people don't realize until they get in the Octagon with me.

"I think the pressure is actually on Rob just because people are expecting him to win. He has his whole family here and he has to deal with all that pressure, not me. It's nothing personal, he has what I want and I'm coming to get it."