Born and raised in a town called San Isidro near the Dominican Republic capital of Santo Domingo, the catcher nicknamed "Beef Mode" was molded by his family, friends and a baseball field all within just two poorly paved streets.
"I'm really blessed because these streets are almost all family," Castillo said about the neighborhood that raised him. "I was born in a baseball family. They played baseball on both sides, my mom's side and my dad's side. The field is right there, so I just have to cross a road, and I'm going to be there."
Castillo is not exaggerating when he says it's almost entirely his family residing on his block. Next door is one aunt, on the other side is his cousin, and so on. When he comes home in the offseason, they all come together and have a three-month-long family reunion.
"It's a pleasure to spend time with them and go to the field and know how everything is going," Castillo said. "Mostly I like just sitting in front of my dad's house with all of my family coming around here and eating, sitting in the street, talking about baseball. That's the stuff that made me happy."
A man of faith, Castillo still attends services led by a neighborhood pastor at the same church he went to as a child. He gets his hair cut at the barber shop across the road he once thought he would run, now owned and operated by his cousin Kelvin. Everywhere you go in this Dominican barrio, you will inevitably find someone in the Castillo family tree.
Castillo's family led him to baseball: As a child, when he saw one of his uncles with a bat and glove, the young Welington would follow him to the field two blocks away. His parents knew early on what they had on their hands.
"Since he was born, he loved baseball," said his mother, Argentina Paulino, through a translator. "He used to sleep with his bat in his bed. He always dreamed about playing baseball."
His father, Federico, described how Castillo would return from practice and grab a rubber ball and bounce it over and over again against the wall across from their house. Castillo also said he would use a water bottle and a piece of wood to play with his friends and cousins, anything to stay connected the game he adored.
Castillo also had a knack for the sport, establishing himself as a tremendous talent when he was young, particularly as a hitter. But he was adamant about playing shortstop, and his stubbornness nearly brought a premature end to his career.
"I was a little smaller and slower, and I didn't want to catch," Castillo explained. "Everyone told me, 'You need to be a catcher, you need to be a catcher.' And I said, 'No, I'm not going to catch.' And I quit baseball when I was really close to signing."
Not being allowed to play the position he favored, Castillo was going to focus on going to college instead, as he was a top student. After a few days though, he found himself drawn back to the baseball diamond, and a scout started badgering him about catching again. The scout had seen Castillo work out as an infielder, but like everyone else envisioned his bat and arm fitting better behind the plate.
"He said, 'Let's do this. Throw a few balls for me to second base.' I said, 'How do I do it?'" Castillo recalled. "I didn't know how to do it, I never caught. He told me to just grab the ball and throw it as hard as I can to second."
Castillo did just that and impressed the scout with his arm, especially considering he hadn't received any training behind the plate. Eventually Castillo was persuaded to attend more workouts at an MLB team's academy. Now showcasing himself as a catcher, almost every team was interested in signing him. At 17 years old, he became a professional baseball player in the Chicago Cubs' system.
The money and lifestyle of a professional athlete hasn't changed him much though, as Castillo still comes back to his hometown. He says he was never in the game for financial reasons, a claim that his parents reinforce.
"The day [Castillo signed] I was working, and his coach called me and told me they want to sign him for $22,000." Federico explained. "Welington said, 'Dad, just take it. I don't care about the money. I just want to play baseball! Later I will take care of the money, but now I just want the opportunity.'"
The first thing Castillo did with his signing bonus was buy the house he grew up in for his parents, so he knew they would always be OK. The next thing Castillo promised to do was to build them a safer and nicer home, even before he got his own place, as the memories of a destructive hurricane still resonated. He fulfilled that promise in 2011, and he is now getting to work on a home for his wife, Kissairys, and their two young boys, 5-year-old Daniel and 3-month-old Jeremiah.
But despite the new digs, he still relishes returning to the same two streets he grew up on, the advice of a former coach ringing in his head.
"Never forget where you come from," Castillo said he was told before his career took off. "I know the U.S. has a lot of great houses, lights, electricity, hot water and security, but I'm never going to forget where I come from."
Kyle Payne is a social media coordinator for the D-backs and contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.