Carragher plays his final game against QPR this weekend.
Houllier told liverpoolfc.com: "His effort is fantastic, he is a competitor and he always liked to have a bit of a race and be better than the other one in training.
"His worth ethic is fantastic and he is, as you know, a very loyal person - loyal to his friends, loyal to his family, loyal to the fans, loyal to the club, which is something that's not very usual now.
"He brought trophies to the club and he also brought heart. Carra is a true Liverpool warrior.
"He is someone who is always happy. His personality, which is always open and really funny, goes well with the town and the fans of the club.
"I also like his generosity. I mean, not many people know how generous he can be. When he had his testimonial he gave all of the money to charity. For the community and for the fans he is someone who is very open and very generous.
"To me and last but not least his sense of humour, because when Carra is around there's always a laugh and there's always a joke going round and he has a great sense of humour - a Scouse sense of humour."