The Dutch defender signed a new one-year contract with the club on Sunday having spent the second half of last season at Hillsborough on a short-term deal. He left Real Zaragoza in the summer of 2013.
"It is fantastic news for us that Glenn has re-signed because he is a top player. He's a fantastic professional," Gray told the club's official website.
"He will be my captain and be an extension of my arm in the dressing room.
"He's a good organiser. He will soon catch up in pre-season. He's come back, looks lean and very, very fit.
"I want Glenn out there every week because of the qualities he can bring on the football pitch."
Former Cardiff and Celtic centre-half Loovens, who made 26 appearances for the Owls last season, said: "I will lead the guys out and give everything for the fans. I'm proud that Stuart Gray has given me the opportunity.
"As one of the older players in the team, it's my job to help the younger players coming through."