Willie was generally a normal whale except for the fact that he simply adored opera, and would sing for any sailors in earshot, leading to the investigations of just how this was possible. Most notably, Tetti-Tatti the Opera Director, who couldn't believe that a whale could actually sing Opera and decided that Willie must have swallowed an opera singer, taking a trio of tough sailors with him to try and rescue the Opera singers so they could perform for him.
Whitey, the seagull, took a newspaper to Willie, all the sea creatures excited for their talented friend as they believe he's going to be discovered and finally have his dream come true. Willie rushed out to meet the ship with Tetti-Tatti and sailors, singing for them and showing the true extents of his talents. The three sailors had no more interest in killing him, wanting to simply listen to him sing, while Tetti-Tatti became more and more frantic, believing that Willie had eaten three Opera singers due to Willie's ability to sing with multiple voices at once. The Sailors repeatedly wrestled Tetti-Tatti away from the harpoon and pin him to listen to Willie.
At first, it seemed that Tetti-Tetti was finally convinced, having become his manager, but later he shot Willie with the harpoon, killing him. Whitey mourned his friend, as Willie's spirit enters heaven. However, he was now able to sing with even more voices, performing for what was implied to be a packed audience, as the golden gates close with a sign which read "Sold Out", having realized his dream after all.
He appears to be very friendly, singing for not only sailors but for his ocean friends, the seals and a seagull. He dreams of singing at the Met and becoming a famous opera star, showcasing his unmatched talent for the world to hear, performing all sorts of operas. He doesn't seem particularly interested in monetary compensation-he just wants to sing his whale-sized heart out for all to hear.
He's a whale-with all that comes with it! He has a huge squishy-looking body, massive head with comparatively small eyes and mouth, boasting a rather unique attribute-having three uvulas in his throat, which allows him to sing with three different voices, even forming different words and notes with each one, leading the Opera director to believe he has swallowed not one, but three opera singers.
Willie made a few appearances among the audience in the series. One of them was "Humphrey in the House", when Humphrey landed on his pile of fish and tried to make a sandwich out of his flipper. Another notable appearance was in "Halloween With Hades", when he was sitting with Willie the Giant when Hades walked by and greeted them. This confused the two, where Willie noted that Hades gives him "the willies".
Willie made a cameo appearance in the episode "O Sole Minnie".