When Doc sees Kermit dancing, after being informed of the frog by his assistant, Max, he's determined to have him as a spokesfrog and won't take no for an answer. Doc previously handled his own commercials, wearing a frog suit.
Doc's dream is to expand his franchise and own 1,000 restaurants. To achieve this goal, Hopper single-mindedly pursues Kermit halfway across the country in his limo, becoming the villain of the film in the process. Doc's methods become increasingly desperate (bringing about a crisis of conscience for Max), hiring mad scientist Professor Krassman to brainwash Kermit (he kidnapped Miss Piggy to lure Kermit to Krassman) and later enlisting Snake Walker and other thugs to kill the frog if he refuses.
Doc's ambitions and ruthless determination are contrasted with Kermit's desire to spread joy and happiness to others. While Kermit's dream "becomes better the more people you share it with", encompassing a broad range of characters, Doc's goals are exclusionary, isolating him even from Max.
During their final standoff in an abandoned ghost town, Kermit makes a final plea to Doc, saying that all he wants is to fulfill his and his friends' dreams and that perhaps if Doc put aside his own selfish intent, he would see that he didn't want to continue his pursuit of the gang. Unfortunately, Doc ultimately decides that if Kermit isn't going to be his spokesman, then he should die instead. Just as Doc's men prepare to finish off the Muppets, Animal plows through the roof of Dr. Bunsen Honeydew's lab, having consumed a large number of Bunsen's Insta-Grow Pills. Animal roars loudly, scaring off Doc and his men, with Max wishing the Muppets the best of luck before he too flees. Doc is never seen again after this incident
Despite the above, in It's a Very Merry Muppet Christmas Movie, The World in which Kermit was Never Born shows that Doc Hopper's Frog Legs is a thriving fast-food restaurant with a franchise in Bitterman Plaza, implying that the chain was able to prosper because Kermit wasn't there to interfere.