I've included a clip from the 1990 award winning film "Tremors" starring Kevin Bacon. You can obviously see where Riot has picked up the concept for their champion.
I'm a little dissapointed, with that being said I have created my own Lore (since Riot doesn't care about lore anymore) to make the story of her a little bit more realistic. Enjoy:
Within the city of Akathia, an ancient city beneath the sand. Vel Koz, the eye of the Void grows old. He sees aging in his once youthful tentacles. He asks himself, is it time to find a predessesor? Vel'Koz up until this point had never considered trying to legthen his legacy, however he sees his time growing short as well as his tentacles growing old. He then calls upon the sands of time to start a summoning ritual. Vel'koz calls upon nine necromancers all seeking knowledge from the all seeing eye of the void. He then promises them his knowledge of the Summoners Rift, in turn they must summon upon a force that has been dormant for over 9000 years. Having only read stories about her, Vel'koz had dreamt about a woman as beautiful as Rek'Sai since he was a young void. He was the only one who possessed knowledge to summon the Queen of the Sands. Vel'Koz, growing old and weak instructed the necromancers to find nine horcruxes, an horcrux for each necromancer, nine making up all of the Sand Queens tentacles. They returned to Vel'Koz with all of the horcruxes making up the Sand Queens tentacles, it had taken the necromancers 113 years to collect all of the pieces. They all gather at the sands of times to begin the ancient ritual, the summoning of the Sand Queen Rek'Sai. Rek'Sai appears, and Vel'Koz can feel his attraction the Sand Queen immediately. Rek'Sai, not ready to settle down thanks Vel'Koz for re-awakening her. She then swears herself to Vel'Koz, only after fighting for 100 years on the Summoners Rift.