The pair helped take the Reds from 12th place in January to a top-six finish and were both rewarded with permanent three-year contracts by owners Fenway Sports Group in May.
It was news that left Agger delighted.
"I was really happy he and Steve Clarke signed their deals. Steve has made a big, big impact and he is really good. I can't say enough good things about him.
"Kenny suits this club. He knows everything about it, and the fans know him. It's positive for the future."