The R&B artist who signed Christina Milian to Radio Killa Records in 2009 was The-Dream.
The-Dream, born Terius Nash, was already known as a singer, songwriter, and producer behind major R&B and pop hits. He founded Radio Killa Records and began working with Milian on her fourth studio album, originally titled Dream in 2009. Their collaboration led to a joint deal involving Radio Killa Records and Interscope Records.
Milian’s project was later retitled Elope, reflecting her relationship with The-Dream at the time. Although the album was planned for release, it underwent delays and ultimately was not released as originally intended. This history can cause confusion because The-Dream was involved both as Milian’s label associate and as a producer and songwriter on her music.
Radio Killa Records was associated primarily with The-Dream’s creative work and label ambitions. The question asks who signed Milian, rather than which major distributor was involved, so The-Dream is the single canonical answer.