Part of it legitimately says 'boop'.
In most games having half an hour of dialogue isn't a big deal, but you have to remember that League of Legends isn't exactly story heavy. New champion Aurelion Sol's dialogue therefore comes with half an hour of taunts, battle cries and odd noises (including three variations on 'boop').
League's last champion, Jhin the Virtuoso, clocked in around 20 minutes, meaning someone really went crazy with this one. The new voice over's length is largely due to it including quotes for many situations that may be encountered on the Rift, such as scoring a pentakill. You can watch the full 30 minutes of dialogue here, if you're so inclined:
Aurelion Sol is a character with a bit more of a colourful history than most -- having first been conceived back in 2013 as a champion called 'Ao Shin' in response to requests for a full dragon champion. Thanks to technical difficulties Ao Shin kept being delayed, and is now finally being reborn as Aurelion Sol, likely as part of the Mount Targon lore rework.
Surrender at 20 scraped this little snippet of in-client lore for Aurelion Sol, though a longer introduction and story will no doubt come later: "Aurelion Sol once graced the vast emptiness of the cosmos with celestial wonders of his own devising. Now, he is forced to wield his awesome power at the behest of a space-faring empire that tricked him into servitude. Desiring a return to his star-forging ways, Aurelion Sol will drag the very stars from the sky, if he must, in order to regain his freedom."
Gameplay-wise, Aurelion Sol is a a medium-range mage with good area of effect damage, who could be a flexible champion in top, mid or even jungle. For full details on all his abilities, check out the champion reveal page here. Aurelion Sol is live on the PBE for testing now.