X is for...

XAVIER ST CLOUD
A Moor who lived in hedonistic splendour throughout the centuries, and who used dubious tactics to disarm fellow Immortals before beheading them. MacLeod first met him in Algiers in 1653 (C21, 'Finale, part one') when St Cloud beheaded his friend, Hamza ibn Mohammed Yaman Al Katib Al Khal (Hamza el Kahir to his mates). The pair also encountered each other during the Napoleonic Wars (D19, 'Double Jeopardy'). After losing his left hand trying to ambush Duncan (A15, 'For Tomorrow We Die'), he later teamed up with James Horton (see H) and a group of mercenaries to track down MacLeod and take his head by unfair means (B14-15, 'Unholy Alliance parts one and two').

Y is for...

Eternal YOUTH
Because an Immortal stops ageing the moment they die their first death, it's obviously more advantageous to be killed in your prime - say anywhere between 18 and 40 - as opposed to dying young (in the case of Kenny) or old. Some Immortals - Duncan among them - have even been known to take a pre-Immortal under their wing and then kill them in order to prevent them from dying outside their prime - in Mac's case, it was done for love (strange way of showing it!). The fact that a pre-Immortal could be left to live a normal life and die of old age is obviously neither here nor there...

Z is for...

ZACHARY BLAINE
An ex-partner of Amanda's (see A). He's promised Duncan's head in return for sparing her life in 1993 after she'd framed him at the end of their earlier partnership. This double-double crossing is something she's particularly good at (A18, 'The Lady and the Tiger').