Snow
The original leader, the legends say that Snow could freeze any water he touched and that his voice sounded like glaciers breaking apart. He was a silver feline, and was an incredible leader. He set Snowclan up for greatness.
Deputy: Dusk (Duskstar)
Apprentice: Jumppaw (Jumpfoot)

Duskstar
The first to get their nine lives in Snowclan, Duskstar was a noble leader and was taught well by Snow. The legends say that Duskstar was perhaps Snow's mate. He was a very strong and large tom.
Deputy: Tigerfang (Tigerstar)
Apprentice: Sandpaw (Sandfire)

Tigerstar
Apparently, Tigerstar looked exactly like a great tiger of the lands far away. Legends say she was large and stocky, with wide shoulders and thick sharp teeth, with white spots on her rounded ears.
She was the first previously-rogue leader.
Deputy: Volefoot (Volestar)
Apprentices: Finchpaw (Finchflight), Tawnypaw(Tawnyfur)

Volestar
A light brown tom, who was reckless with his lives and died at a younger age than most leaders. He was a good leader, though, and was kind at his best and territorial at his worst.
Deputy: Patchtail (Patchstar)
Apprentice: Whiskerpaw (Whiskermuzzle)

Patchstar
A white and brown patched tom with brown eyes, and he enforced the rule that kittypets should be banned from clan life. This code never went through, and Snowclan cats are sometimes bitter about it.
Deputies: Lionpelt, Snowcrescent (Snowstar)
Apprentice: Kinkpaw (Kinktail)

Current leader:
Snowstar
A white fluffy tom with yellow eyes, the littermate to Stormclan's current leader, Stormstar. He is territorial and aggressive, but a cool and calculating leader, pushing his clan to greatness.
Deputy: Bluebird 
Apprentices: Spottedpaw (Spottedshine); Brightpaw (Brightcreek)