Templeton is a selfish character. He only cares about himself. And food. He loves food so much he does stuff for Charlotte to get more food. One example is when he went to a fair to stuff his face and get more words for Charlotte to write in her web.
Even though he is greedy and selfish, he is important because he gets words for Charlotte. So he is still important to the story.
Here is my Wordle about Templeton