"The Leopard was launched in 1790. As a 50 gun ship, she was already nearly obsolete, being too small to stand in the line of battle and unsuitable as a cruising ship."
In the Canon
Leopard - "the horrible old Leopard" - first appears in The Mauritius Command, where (as in real life) she takes a minor part in the campaign. Later, in Desolation Island, Jack Aubrey commands her on a voyage to Australia. By the end of the voyage in The Fortune of War she is in very poor condition having survived near shipwreck. She underwent makeshift repairs on Desolation Island but, as Aubrey puts it in The Surgeon's Mate, "the ice had given her frame such a wrench that she could not carry any piece of metal -- no good to man or beast: only fit for a transport." The ship's actual history also causes significant difficulties when negotiating with American whalers for assistance in repairing the rudder.
Later in The Letter of Marque, Stephen Maturin takes passage to Sweden aboard the Leopard, now converted to a transport. Again the voyage is eventful with a grounding necessitating the repair of the rudder. However, Maturin is recognised as an old Leopard and treated with respect for the second half of the voyage.