кто-либо

Pronoun

 * 1) (indefinite pronoun) anybody, anyone, somebody, someone (implies one does not care who, or does not have any particular person in mind)

Usage notes
The particle -либо is used more often in writing, while -нибудь is used more often in spoken speech. Apart from this, they are largely synonymous, with their use subject to the stylistic and idiosyncratic preferences of individual speakers.