Kristin Hayter (born June 17, 1986) is an American singer and pianist. She started releasing music in 2017 and performed under the stage name Lingua Ignota (Latin for "unknown language"). In 2023, citing the unhealthiness of reliving her trauma through her performances, Hayter retired the Lingua Ignota project and adopted a new persona under the moniker Reverend Kristin Michael Hayter.

Her professional music career began in 2017 with the self-released albums Let the Evil of His Own Lips Cover Him and All Bitches Die, which spread through word-of-mouth. Hayter's music caught the attention of Profound Lore Records, who re-issued All Bitches Die and released her third studio album, Caligula, in 2019, which was met with universal critical acclaim. Her fourth album, Sinner Get Ready, was released in 2021 on Sargent House and received more widespread critical acclaim. Her work as Lingua Ignota drew from her experiences as a survivor of domestic violence for musical and lyrical inspiration, and she describes her music as "survivor anthems". Her debut album as Reverend Kristin Michael Hayter, Saved!, came out in 2023.

Hayter was born in Del Mar, California, in 1986. She felt like she didn't fit in in Southern California and was often bullied. About her hometown, she said: "I think of [Del Mar] as a sort of hell in the way that I was so different than everyone else when I was growing up and couldn't situate myself, couldn't find myself there at all." Hayter was raised Catholic and was educated in parochial schools until the sixth grade, when she entered public school. A teacher noticed her voice's natural vibrato when she was eight years old, which led to her becoming a church cantor, singing every week at her local church and beginning classical voice-training lessons. Despite a religious upbringing, she considered herself to be an atheist for several years starting as a teenager. However, in 2019, Hayter claimed she had "renounced her teenage atheism" and had become particularly interested in Roman Catholic iconography and concepts of divine retribution.

Hayter studied interdisciplinary creative arts at the School of the Art Institute of Chicago, earning a Bachelor of Fine Arts, and earned a Master of Fine Arts (MFA) degree in Literary Art from Brown University in Providence, Rhode Island, in 2016. She is also classically trained in piano and voice. Her undergraduate thesis, titled Architect and Vapor, deconstructed Johann Sebastian Bach's The Well-Tempered Clavier, and centered its poetry component on anorexia, a disorder Hayter had for over a decade. For her MFA thesis, titled Burn Everything Trust No One Kill Yourself, she created a 10,000-page manuscript (a page count selected because it was approximately Hayter's weight in paper) linking real-world examples of misogyny in music with her own personal life using a Markov chain. In her own words, it was composed of "lyrics, message board posts, and liner notes from subgenres of extreme music that mythologize misogyny, […] [and] court papers, audio recordings, and police filings from my own experiences of violence." In addition to the manuscript, her interdisciplinary performance included music and a black-and-white video projection with footage of serial killer Aileen Wuornos and burning buildings.

In high school, Hayter played in various metal garage bands with her friends.

Kristin Hayter began releasing music in 2017 under the moniker Lingua Ignota. Literally translating to "unknown language", the name is derived from the sacred constructed language Lingua Ignota created by the German Christian mystic Hildegard of Bingen. She chose this name because of her interest in glossolalia or ecstatic language, relating it to the idea of a "possession" or God speaking through a body. She said, "I'm trying to construct something that speaks the unspeakable, and so I use this sort of amalgam of musical devices to make my own sonic language which is meant to also be ecstatic or outside the self." Hayter released her first album under the name Lingua Ignota on Valentine's Day 2017. Titled Let the Evil of His Own Lips Cover Him, all of the proceeds were donated to the National Network to End Domestic Violence not-for-profit organization and combined original compositions used in her MFA thesis Burn Everything Trust No One Kill Yourself with a cover of the Inner Circle song "Bad Boys", famous for its use as the opening theme on Cops. There are about 10 songs from Hayter's Burn Everything Trust No One Kill Yourself thesis performance that may be released one day.

Four months later, Lingua Ignota self-released its second album, All Bitches Die, through Bandcamp in June 2017. The album consists of four "murder ballads" loosely inspired by Angela Browne's 1987 book When Battered Women Kill, a study of victim violence. Hayter did not plan to tour in support of the album and only expected to sell a few copies; however, word-of-mouth buzz surrounding All Bitches Die eventually made its way to Chris Bruni, owner of the Canadian extreme metal independent label Profound Lore Records. Profound Lore reissued All Bitches Die with updated artwork and a bonus track in 2018. Hayter said of the label: "Lingua Ignota is not a neutral project by any means and I've been asked to tone it down in various capacities since I've started. But Profound Lore only encouraged me to remain uncompromising and brutal, and that was ultimately what sold me to them as a label. I feel like they really believe in my work and won't ask me to dilute it to make it more fashionable or palatable." Lingua Ignota opened for experimental metal band The Body during their North American June–August 2018 tour, who Hayter credits for welcoming her into the experimental metal scene. The Body was touring in support of I Have Fought Against It, but I Can't Any Longer., an album that features guest vocals from Hayter.

After All Bitches Die, Lingua Ignota began working on a full-length album of cover songs that were reinterpreted in her unique music style, often with re-written lyrics. Songs from this session included Eminem's "Kim" and Foreigner's "I Want to Know What Love Is". A split EP with The Rita was released in 2019 that featured covers of Dolly Parton's "Jolene" and Scott Walker's "The Girls from the Streets". With the covers album still unannounced, Lingua Ignota released its third studio album, Caligula, through Profound Lore on July 19, 2019. The album is about one of her abusive relationships, specifically about "speaking out about abuse and feeling invalidated, and people who I thought were my friends no longer being my friends, and the crushing experience of how that feels."