关于 called 和is called

关于 called 和is called
今天二模的一道语法选择,我分不太清楚：Anyone who has a dog as a pet will tell you why the dog ()man's best friend. 请问是选择is called 还是called ?别人都是选is called ,但是我有个疑问,以前好像看到过一个句型是aman called Zhou Jian,我知道是过去分词作定语,那怎么看呢