Henk

Henk

Default skin

Swan Henk

Unlocked by completing Swan Henk's Bonus

Summer Henk

Unlocked by completing Summer Henk's Bonus

Blue Blaze Henk

Early Access Reward. Thanks for the support!

Hallowhenk

Unlocked during Halloween

Henkdolph

Unlocked by completing Henkdolph's Bonus

Santa Henk

Unlocked by completing Santa Henk's Challenge

Action Henk

Unlocked by completing 90's Henk Redemption

Plumber Henk

Unlocked by obtaining the "Buttslide" achievement (removed)

Action Hank

Unlocked by completing Action Hank's Bonus

Rainbow Henk

Unlocked by getting a rainbow medal on all levels

Henk VS Game

Unlocked by completing all campaign levels in a single session. (no city & bonus)

Champion Henk '15

Winner of the 2015 Action Henk World Championships!

Team Henk #1

Winner of the Action Henk Team Tournament!

Team Henk #2

Second place on the Action Henk Team Tournament!

Caster Henk

TrueBlackShark special skin for hosting the tournaments

Champion Henk '16

Winner of the 2016 Action Henk World Championships!

Twitch Henk

Unlocked by pressing the key when a stream is announced on the main menu

Skins written in red are not unlockable in-game.
pictures taken from Tom Rutjens's website & in-game