The 49ers are smitten with Reuben Foster.

And their love affair began well before their draft room resembled a winning Super Bowl locker room after they selected the Alabama inside linebacker in April.

More than a year earlier, before the 2016 draft, 49ers vice president of player personnel Adam Peters was studying video of Alabama inside linebacker Reggie Ragland.

Peters, then in the Broncos’ front office, liked Ragland, the SEC Defensive Player of the Year who became a second-round pick. But he loved Foster, his teammate who wasn’t draft-eligible.

“This guy (Foster) is running past (Ragland) on every single play and making it,” Peters said. “It was like ‘Forget about that guy — who is that guy?’ And Reggie Ragland is a very good payer in his own right, don’t get me wrong.”

Peters is hardly alone. Both he and general manager John Lynch have labeled Foster, the No. 31 pick, their favorite player in the draft. (This, despite using the No. 3 pick on Stanford’s Solomon Thomas.) And it’s not just the front office. Linebackers coach Johnny Holland has termed Foster one of the best inside-linebacker prospects in the past 10 years.

For his part, Lynch, who admits he can’t suppress a smile when discussing Foster, seems incapable of not gushing about his draft crush.

“I don’t want to make undue expectations on this kid,” Lynch said last week on KNBR, “but I have full confidence that he’s going to have a terrific career. He has it all to me.”

Some NFL teams were highly skeptical, but the early returns suggest the 49ers’ swooning over Foster is justified. Foster was a consensus top-10 talent, but he nearly slipped out of the first round because of concerns about his surgically repaired shoulder and his character.

It’s premature to assess if the 49ers were right to rank him as the third-best prospect in the draft, but this can be safely said: They remain smitten.

Foster was medically cleared just before training camp and he has flashed the ability that made him the winner of the Butkus Award, given to the nation’s top linebacker, while practicing with no restrictions.

Foster already has a team-best three interceptions in four practices and a few other highlight-reel plays. On Monday, he was a blur who bolted into the backfield to blow up a sweep play to running back Raheem Mostert.

“He’s got great instincts — just a real knack for being in the right place at the right time,” quarterback Matt Barkley said. “… I remember seeing him play at Alabama — and seeing the hits he can deal can be pretty devastating. He’s taking it easy on our guys right now, but I think when preseason games come — he’ll be lighting it up on the field.”

Foster’s physicality was part of the attraction for Lynch, a hard-hitting safety who spent 15 seasons playing with Foster’s reckless abandon. Lynch has said Foster’s style — best exhibited in college when he flattened LSU’s industrial-size running back Leonard Fournette on kickoff coverage — will be infectious.

Defensive quality-control coach DeMeco Ryans, 33, a linebacker who was voted to two Pro Bowls in his 10-year career, noted Foster has a quality many players only talk about possessing.

“He definitely hits a lot harder than I did,” Ryans said. “His intention is to run through (people). A lot of people talk about it. ‘We want to run through. We want to be physical.’ Yadda, yadda, yadda. Reuben actually does it. That’s what’s unique about him.”

Foster is undeniably gifted and apparently healthy. Still, there are those questions about his character: He will have to prove he possesses the focus and discipline to succeed in the NFL.

The reported a team with a top-15 pick didn’t have Foster on their draft board because of his “immaturity” and “issues with life skills.” And that was before he failed a drug test and was kicked out of the NFL combine for getting into a reportedly “heated altercation” with a hospital employee. Two months later, Foster’s draft party was sponsored by a tobacco and marijuana vaporizer company.

The 49ers hosted Foster for a pre-draft visit and later sent team pastor Earl Smith and Keena Turner, a former linebacker involved in their player-engagement department, to visit with Foster for two days in Tuscaloosa, Ala.

The team learned more about Foster’s challenging childhood and how it shaped him. In 1996, when he was 19 months old, Foster and his mother were shot by his father, Danny. They both survived. Danny Foster went on to spend 16 years as a fugitive before he was arrested. Foster has spoken with his father, but they do not have a relationship.

In multiple stories since Foster left Alabama, Nick Saban, his college coach, has said Foster will need an NFL environment with a solid “structure.”

The 49ers believe they have a strong support system that includes Holland and Ryans, former NFL linebackers who can relate to the pressure of being high picks. (They were both drafted in the second round.) In addition, Ryans also attended Alabama and got to know Foster when he was still playing for the Tide.

On Sunday, Foster termed Holland a “father figure” and said Ryans was “like a brother.”

“He came on his (pre-draft) visit here and we just felt ‘He fits us,”’ Holland said of Foster’s connection with the franchise. “‘He can fit in with us. We can offer a lot to him as a mentor, and he can offer a lot to us as a player.’ It was one of those deals that was meant to be, it felt like …”

“As a 23-year-old, there’s a lot of things that he hasn’t experienced yet and he’s willing to listen to experiences I’ve been through. That DeMeco has been through. And he’s always willing to learn and listen. That’s what exciting about him: How much better we can make him as a football player and as a person.”

Foster, who has two children, says he’s intent on becoming a “better “man, father and teammate.” And he believes the 49ers have the same goals for him.

“I’ve felt much love, much loyalty,” Foster said. “It’s not just a business here. I’ve felt relationships in this program.”

Foster talks with a genuine enthusiasm and it’s hard not to smile at some of his answers in media sessions.

On Sunday, when asked about playing with All-Pro linebacker NaVorro Bowman, his eyes widened: “I was worried at first. I was worried. Because if you look at Bo — and you look at me — he’s a man. That’s a man. Did you see his arms?”

He also had this explanation for his training-camp interceptions: “I guess the ball’s got a thing for me. I don’t have a thing for the ball.”

Later, when a reporter spoke with him off to the side, Foster’s mega-watt smile momentarily vanished when asked being viewed as “bad guy” before the draft.

“I’m a great guy. An awesome guy, you feel me?” Foster asked, his smile returning. “I love you; you love me. To know Reuben is to love Reuben.”

Three months into their relationship, the 49ers agree.

Eric Branch is a San Francisco Chronicle staff writer. Email: Twitter: @Eric_Branch

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