A Brief Anime History of The Himbo
Lupin III: Part Two, the thief was a goofier and objectively less evil character; by 1979's The Castle of Cagliostro, he was practically a gentleman like his great-grandfather. Lupin's signature stupidity and goofy kindness won him a massive following which has endured in the decades since, and as the series continued, more writers leaned into those parts of his characterization to make him into the himbo we know today. Even if Monkey Punch himself wasn't a fan of the character's changes, (“I wouldn't have had him save the girl,” he notoriously said of Cagliostro, “I would've had him...
Source: animenewsnetwork.com