"Ay, uncle Fonz!" Spike says, rolling up to Arnold's on his bike and dressed exactly like the Fonz. The mini version of Fonzie punches Henry Winkler's shoulder in greeting.

"Ay, how ya doing, Spike?" Fonz says, slugging Spike on the shoulder right back before turning to introduce Spike to Richie.

In the episode "Not With My Sister, You Don't," Happy Days introduces Fonz's nephew Spike for a very special occasion — Joanie's first date. Spike, naturally, is the fella who ends up taking her on it, despite the Cunninghams' misgivings.

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Of course, Happy Days as a series ends with Joanie marrying a different member of Fonzie's family, his cousin Chachi. Their relationship trod the same tension as Joanie's first date with Spike.

For this reason, fans with fuzzy memories often confuse Spike and Chachi, thinking they were intended to be the same character, with Chachi appearing later as the grown-up version of Spike. As recently as 2003, fans were still posting on at least one message board asking, "Were Spike and Chachi the same character?"

So, here's a breakdown so you can get the Fonzarelli family tree straight in your mind.

Spike is Fonzie's nephew. He appears in the second through the fourth seasons of the show, and he's played by an actor named Danny Butch.

Chachi is Fonzie's cousin. He appears in the fifth season through the end of the series, marrying Joanie in the episode that was meant to be the end-cap to the entire series.

The thinking was that Spike would be introduced and grow to be as popular as Fonzie. But Garry Marshall failed to strike gold twice, and Spike did not become a major heartthrob like his uncle.

Scott Baio proved the sitcom could still introduce popular characters, though, because when he joined the cast, he became a teen idol. 

However, it's possible that Spike might have become more popular if there had been more publicity done to get the audience pumped up for his character. Apparently, there was practically no info for fans to get to know Danny Butch, the actor who was primed to be the next Fonzie.

In 1976, after Butch returned to Happy Days to appear in a few episodes in the third season, four different fans of the show were so curious about who this kid was that they wrote into the TV mail section of their local paper, The Courier of Waterloo, Iowa. "Could you please tell us where to write 'Spike' on Happy Days and give us information on him, if possible?" they asked.

The Courier responded with an address to reach Danny Butch in Hollywood, explaining "ABC has not serviced a biography on him yet." The P.R. machine could have made the kid a contender.

Not much is known about Butch beyond his few appearances on Happy Days, but he did join a cast reunion in 2005, so we have to assume there were no hard feelings about living in the shadow of the more popular Fonzie types on the show.