Kaj Erik Persson Hassle (born 26 August 1988) is a Swedish pop singer and songwriter. His career started in 2008 with his first single, "Hurtful", which eventually reached No. 11 in Sweden and peaked at No. 2 in Denmark. His most successful single to date, "No Words", reached the Top 10 of the Global and U.S. Spotify Viral Chart and achieved Gold certification in both Sweden and Denmark.

Hassle, who signed to Island Records in 2009, has released four albums, most recently Innocence Lost in January 2017. Aside from solo work, he has cowritten a number of songs for other singers, including Shakira and Rihanna's "Can't Remember to Forget You". He won a Danish Gaffa award and two Swedish awards, a Grammis and a P3 Guld.

Saluted as "the new, young Robbie Williams" upon his international debut, Hassle has been described as "a voice steeped in simmering sultry soul, a funked-up sense of international swagger, and unbridled lyrical honesty."