She was born Kai Anne Inge Fischer in Prague (then Czechoslovakia), the daughter of a senior public servant. After the war, Kai's family moved to Munich where she completed her matriculation and took on her first job as a stenographer, progressing from there to photo model and mannequin. Though lacking any genuine dramatic training, Kai made her performing debut on the stage in cabaret at Walter Novak's Schwabinger Brettl (then something of an institution in Munich's nightlife). By the mid-50s, she began acting on the screen.
The hot-blooded redhead found herself quickly typecast as seductresses, ladies of easy virtue, hard-boiled publicans or gangster molls (like her Bettina in
Das Wirtshaus im Spessart (1958)). She would occasionally pop up in international productions like the tongue-in-cheek, campy period drama
The Hellfire Club (1961) or as Countess Polensky in the Johann Strauss Jr. biopic
The Waltz King (1963). By and by, Kai seemed rather more at home as robust characters in popular
Edgar Wallace adaptations like
Room 13 (1964),
The Inn on Dartmoor (1964) or
The Monster of London City (1964). From the mid-60s, sometimes billed as 'Kay Fischer', she also made a slew of exploitation films with the emphasis firmly on sex, as well as assorted European potboilers, from spaghetti westerns (
Bullets Don't Argue (1964)) to low budget shockers (
Island of the Doomed (1967)) and erotic comedy (
Die sündige Kleinstadt (1975)).
In the mid-60s, she began to transform her image by devising the character of a female sleuth for her own series,
Die Karte mit dem Luchskopf (1963), thereby entering a genre which had previously been the domain of men. In 13 episodes, her Kai Fröhlich solved cases by going undercover, her agency ostensibly run by an imaginary Mr. Luchs (which translates to Lynx and also refers to her detective's visiting card with the emblem of a lynx head).
Kai's image transformation continued through the 70s and 80s with more serious roles in the bleak
Wim Wenders drama
The Goalie's Anxiety at the Penalty Kick (1972) and as guest star in TV episodes of
Der Kommissar (1969),
Derrick (1974) and
Tatort (1970). Also on television, she found popularity as the circus dompteuse Tiger-Lilli in the miniseries
Salto mortale (1969). In 1970, she released an album of 'naughty songs' under the title Kai Fidelity. In 1984, she operated several photography shops in Munich and has also authored crime novels under various pseudonyms.