The Norwegian forward joined the Potters last month from Villa on a loan deal until the end of the season and netted his first goal in Saturday's 3-2 win over Sunderland.
Pulis told the club's official website: "I spoke to Martin before we did the deal. He was the one who convinced me that he would be a great signing for this club.
"He told me that he's a smashing, big fellow; a gentle giant in lots of respects, but if you get him at it and motivated, he's as good as anybody.
"John has been fantastic. The great thing is that he has become a firm favourite in the dressing room and the other lads love having him around.
"John's got great experience of playing at the highest level across Europe. His technique is excellent and he has a great sense of awareness. I am confident that he's going to be a great acquisition."
Source: PA
Source: PA