Kenneth "Ken" Calvin is Cody's doll/homosexual boyfriend. Cody actually believes that Ken is a real person, and has had sex multiple times. Bowser Jr. and Joseph think Cody is weird and gay because he has sex with Ken multiple times. Cody often exhibits a little to much public affection for the doll as for example in Bowser Junior's Package, he can be seen on Facebook "bath time" with Ken with bubbles (implied cum) on his mouth and on Ken's genitals.
The Ken doll Cody originally bought is different from the one used in later videos. The Ken doll Cody brings along with him now is based on the Hawaiian Vacation Ken or Toy Story 3 Ken.
In Bowser Junior's Fireworks!, he was attached to the fireworks and Bowser Junior, Cody, and Joseph thought he died but he survived.
In Bowser Junior's Lottery Ticket!, when Cody asks Ken what Ken would do with $1 Billion, Ken imagines shooting Cody with a gun. It is revealed that Ken hates Cody, likely because Cody uses him a a sex toy.