The beautiful and deadly champion known as Sivir has been a favorite of League summoners for close to a decade. A soldier-for-hire outside of the Fields of Justice, she is the embodiment of a highly successful mercenary on modern day Runeterra. Sivir has little interest in the ''cribbage sheets'' - as she calls them - of League influence bartering. Instead, she is motivated by material wealth and riches, and she is paid handsomely for her services. Sivir is one of the wealthiest individuals found anywhere on Valoran. Sivir owns multiple residences in a number of different city-states, as well as ownership stakes in a number of businesses all across Valoran. Her detractors, either envious of her success or acrimonious of her flexible morality, have begun to use Sivir as a symbol of what is wrong with the mercenary nature of the League. Sivir dismisses her critics, saying that while her personal code of ethics is less ruthless than her competitors, ''Everyone has a price.''

Sivir has earned many titles and accolades throughout her illustrious career, but the one she held until recently was ''Battle Mistress of Noxus''. Now she is simply known as ''The Battle Mistress'' after breaking her contract with the Noxian High Command. Sivir dared to object to the Noxian war against the peaceful island state of Ionia, though less about the morality of the issue than the planning behind it; her predictions of a bloody stalemate came true when the Ionians held off the relentless assaults of the Noxians. Claiming that the Noxian High Command had lost its direction, she left Noxus and made her services available to the Institute of War. The Noxian High Command has sent a number of contracted assassins to deal with its rogue mercenary, but none have delivered her or survived.

『Time and time again, Sivir proves that she has earned the right to call herself 'The Battle Mistress'.』 -- Jax