Which Assassin's Creed game first introduced the hidden blade as a retractable wrist weapon?

The original Assassin's Creed game first introduced the hidden blade as a retractable wrist weapon. Altaïr uses it for discreet assassinations, making the blade one of the series' defining pieces of equipment.

The weapon is associated with the Levantine Assassins and is concealed beneath a bracer. Earlier fictional lore says removing a finger helped users deploy certain versions, but later games revise and expand that tradition. Assassin's Creed II depicts Leonardo da Vinci modifying Ezio's blades so a finger is no longer sacrificed.

The hidden blade appears in many eras, with changes such as poison mechanisms, double blades and rope-dart attachments. Despite those variations, its first playable appearance is in the 2007 debut title.