Alastair Ruadh MacDonnell, Scottish spy (b. 1725)
Alastair MacDonell of Glengarry (ca 1725–1761), also known as 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, he continued to be active in Jacobite plotting but became a British government agent. This remained secret until 1897 when Scottish historian Andrew Lang confirmed his identity as "Pickle the Spy".

He became 13th chief of Glengarry in 1754 and died unmarried in 1761, when he was succeeded by his nephew Duncan.