One who states positively

• Plaintiff, e.g
• Plaintiff, e.g.
• Accusatory one

Wiktionary Word definitions in Wiktionary
n. A person who alleges, especially one who does so formally

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Alleger \Al*leg"er\, n. One who affirms or declares.

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1570s, agent noun from allege . The Latinate form, allegator (1680s) rarely was used, for some reason.