The 30-year centre-back joined the Reds reported £4.2million move from Augsburg to Anfield with Klopp having been a long-time admirer.
"At the end of last season I knew that if we decided to take somebody in this position he was the one I wanted," Klopp told the club's official website. "Now I'm really happy with the options we have got at centre-back.
"I've seen up close for three seasons how good his performances in Germany have been and last season we got chance to see him against us - and a lot in preparation - for our [Europa League] games against Augsburg.
"The last time he played against us at Dortmund they had 10 men and he defended really well to help them get a clean sheet and a win.
"He has had chances to move to some very big clubs but showed loyalty to Augsburg and now we've beaten some big teams for him to come here."