Rata is the Ferengi second officer serving under DaiMon Bok when Bok presents Picard with the derelict Stargazer as part of a hidden plan of revenge.
Rata appears in The Battle. He serves aboard Bok's Marauder beneath the first officer, Kazago, and beams aboard the Enterprise-D with them for the meeting at which Bok announces his gift of the USS Stargazer.
Like Kazago, Rata is appalled to learn that the ship is being handed over without any payment, a gesture no Ferengi would normally consider. Neither officer knows that Bok has spent a fortune on a forbidden thought-maker in order to torment Picard for the death of his son at Maxia.
Once the scheme is exposed, Kazago relieves Bok of command for engaging in a venture with no profit. Rata is a small part, but he helps establish the early picture of Ferengi crews as ruled strictly by gain.