Alastair Ruadh MacDonnell

Alastair Roy MacDonell of Glengarry (ca 1725–1761; Scottish Gaelic: Alasdair Ruadh MacDomhnaill, was the 13th chief of Clan MacDonell of Glengarry. Brought up as a Catholic and largely educated in France, he was arrested in November 1745 on his way to join the 1745 Jacobite Rising.

After his release from the Tower of London in 1747, MacDonell became a highly damaging mole for the Hanoverian government inside the Jacobite movement. In addition to delivering fellow Jacobite leader Dr. Archibald Cameron of Lochiel to the government, resulting in the latter's 1753 execution at Tyburn, Glengarry is also believed to have been used as an agent of influence to sow dissension within the Jacobite movement over the missing Loch Arkaig treasure. Some sources allege that Glengarry simultaneously "helped himself" to the treasure, but even if he did so, he still could never afford to properly rebuild Invergarry Castle, which had been severely damaged by government troops during the aftermath of the rising.

He became 13th chief of Glengarry in 1754, died unmarried in 1761, and was succeeded by his nephew Duncan. His espionage career remained carefully guarded government secret until 1897, when Scottish historian Andrew Lang confirmed Glengarry's secret identity as "Pickle the Spy".