Lieutenant Kif Kroker is a fictional character in the animated television show Futurama. His surname is a pun on "croaker", possibly a reference to his amphibian appearance and physiology. He is the assistant to Captain Zapp Brannigan and first officer of the Democratic Order of Planets (DOOP) starship Nimbus. His frustration with Brannigan's arrogance and general incompetence in Season 1 leads him to be a disaffected, indifferent, sardonic lackey, although his personality differs greatly in later seasons. In an ironic twist, Zapp thinks Kif to be his best friend and confidant, whereas Kif sees him as an incompetent jerk.

Kif has three nipples, and is able to shed his skin when necessary. His skin can also change colors to blend in with his surroundings like a chameleon (though he has some difficulty controlling it, as shown in "Where the Buggalo Roam"), and is somewhat elastic. He can inflate his head to gargantuan size to frighten away predators. His hands and feet are equipped with suction cups, allowing him to climb walls much like a gecko. Kif has no skeleton; his body has a system of fluid-filled bladders instead of bones.

In Season 3, Kif begins dating Planet Express employee Amy Wong, whom he met aboard the starship Titanic in "A Flight to Remember".

While dating Amy, Kif's character is fleshed out a great deal; it is revealed that he is actually an extremely sensitive, shy and timid creature. It took him months to work up the courage to ask Amy out for a date, and even then it was only through Zapp that a date was finally arranged. His non-confrontational personality makes it difficult to stand up to Zapp, and so he complains about him to Leela (much to her consternation) and anyone else who will listen. When actually in command of a subordinate, however, he'll become quite a martinet, once telling Philip J. Fry "Mix those mixed nuts! I see two almonds touching!"

He is also revealed to be a very romantic man (even though he is an amphibious reptile-creature), if somewhat lacking in self-confidence, and it is shown that he and Amy truly do love each other. Amy's parents are not enthusiastic about him, often referring to him as "squishy green alien" which he literally is, because his body is made of fluid-filled bladders. In contrast, an earlier episode (in which the two met) actually showed Amy's parents' approval of Kif, possibly because he was a captain at the time. While many times Kif does not seem masculine, in "Three Hundred Big Boys" Kif fights off 2 Spidarian soldiers until Zapp runs over him in a jeep-like craft, showing that he has some proficiency in armed combat. Nevertheless, it seems that Kif can't possibly get the approval of Amy Wong's parents, as they want their daughter to marry their ranch hand, a buff, macho cowboy, along with every other male they happen to come across, even a "strong man like Zapp Branigan". The males of Kif's species can carry and bear young, as Kif did in "Kif Gets Knocked Up a Notch". Kif explains that his species can exchange genetic information even through simple touch. This occurs during a "receptive phase", which happens when a member of his species is deeply in love. It is unclear whether this is their only form of reproduction, or just an ancillary method. In "Amazon Women in the Mood", he ran away from one of the women he was assigned to, and in "Where the Buggalo Roam", he misunderstood what the term "making love" was.

Professor Farnsworth's inter-species DNA maternity testing machine ("even I laughed at me when I built it" he explains) reveals the "mother" of Kif's young to be Leela, though Kif explains that the true parent is the one who inspired the original feelings of love, regardless of the DNA donor. The word used for this "true parent" is smizmar, a pun on the well-known Vulcan phrase "diftor heh smusma" ("live long and prosper"). At the baby shower held for Kif, Amy leaves him suddenly, finding herself unable to make the sacrifice of her lifestyle for parenthood, only to change her mind in the end and return to him in time for the ancient birthing rite on Kif's homeworld. He gives birth to a spoor of tadpoles and explains to Amy that the babies will return in twenty years, and Amy decides that by that time she will be ready for parenting. At the end of the episode, a one eyed tadpole (one of Kif's) swims around, the result of Leela's DNA.

Promotional storyboard releases for the second Futurama movie, The Beast with a Billion Backs show Kif and Amy formalizing their relationship in what appears to be a wedding, with Zapp as the best man.