Erovan M'Rill, aka the Orion Sleeper, was a male Caitian with a fuzzy gray tail and a Section 31 operative.

By 2379, M'Rill had been planted aboard the Orion Syndicate freighter Caedera as a helm operator to monitor its actions; fellow operatives Dietz and L'Haan activated him when Presidential Chief of Staff Koll Azernal and Secretary of Military Intelligence Nelino Quafina plotted to use the Caedera to ship additional contraband shipments intending to implicate the Tholians in the construction of nadion-pulse cannons on Tezwa. M'Rill held a knife to the throat of Quafina when he came aboard to negotiate with the Caedera's commander, Trenigar, obtaining DNA traces that later linked him to the entire operation. M'Rill also scanned every cargo container, then rescanned and checked the inventory against his master list after making the drops to track which shipments went to which freighter. The operative was able to relay this intelligence back to his superiors via the use of a combined signal tap and subspace communications device hidden in a data relay repair hatch at the end of an access crawlspace in engineering - the signal tap was able to monitor and copy all the sensor readings, subspace communications, and transporter records for the ship, which Trenigar usually wiped before entering port.

After the cargo shipments were captured and the plot discovered by the USS Enterprise-E, the Caedera was scheduled to be scrapped; M'Rill, under the pretense of discovering a mutiny, lured Trenigar to ship's engineering, where he killed the Captain after having disposed of the entire crew. M'Rill dumped the bodies into space, then abandoned the freighter until it was picked up by the USS Republic. (TNG novel: A Time to Heal)