What a mystery he is! Chirpy Robbie, the impish dreamboat. Vulnerable Robbie, the reticent idol. Mad-for-it Robbie, the grinning, gyrating superstar bestriding the pop universe.
The former Take That! posterboy-turned-credible FM radio mainstay remains a beguiling bundle of contradictions. It was no surprise then that the thousands strolling towards Lansdowne Road last night for the first of two soldout concerts were a diverse lot: sunburned teens milled among louche twentysomethings, faintly-embarrassed boyfriends sloped behind packs of boisterous youths in replica Celtic FC shirts.
A few stragglers sipped beers, but there was little overconsumption: this was to be an evening of squeaky clean fun rather than alcohol-fuelled debauchery.
Chomping a burger outside the Lansdowne Hotel, Helena Ryan from Clonmel struggled to define Williams's appeal.
"Why is he so popular? I don't know, really. I'm not such a huge fan of his music. But there's something likable about him. He seems like a normal person, a real human being."
Among the crowds drifting along Baggot Street, Jennifer Crawley and her daughters, Katie and Megan, from Santry, proved more exuberant.
"He's gorgeous, really. And he knows how to rock," beamed Ms Crawley. "He's not wimpy like Westlife or any of that shower. He writes proper songs and plays proper music."
Williams has achieved the seemingly impossible, escaping the boyband ghetto to strike it rich with a more lucrative mainstream audience.
Most of the adolescents making their way to the show were accompanied by older siblings. They seemed surprised that anybody might think of comparing Williams to the current crop of boyband hopefuls.
An estimated 40,000 people attended last night's performance. A second concert takes place tonight with Williams due on stage shortly before 9 p.m.