After several weeks of negotiations, Ruggeri signed for Atletico at the beginning of July for €17m.
This morning, the Italy international stated to the club's media channels: "It's a great honour for me to join this family; it's a dream come true. I'm thrilled to have joined such a fantastic club, so rich in history. I can't wait to start training and playing.
"When my agents told me about Atlético's interest, I immediately said yes , I had no doubts. It's a huge opportunity that I couldn't pass up.
"I've often played as a winger in a five-man defence, but I can also adapt to a back four or as a left centre-back in a three-man defence. I like to attack and fight for every ball. That's where my nickname, 'Tigre,' comes from.
"I never hold back, I always fight and try to give my all for the team."
Ruggeri added, "Working with Cholo is a dream come true. He's a great coach and a special person. I spoke to him a few days ago and immediately sensed his passion."