Sombr's career began in his Manhattan bedroom in the early 2020s, where the teenage singer-songwriter built a viral online following with moody, lo-fi recordings that have since propelled him into the mainstream. Born Shane Michael Boose and raised in New York City, he started writing and producing his own songs as a young teenager, blending bedroom-pop intimacy with alternative-rock and dream-pop influences.

He first broke through online with a string of viral singles, most notably "Caroline" and "Back to Friends" (both 2024), which racked up hundreds of millions of streams and earned him a major-label deal with Warner Records. His emotive vocal delivery and confessional lyrics drew comparisons to artists like Steve Lacy, The Neighbourhood, and Cigarettes After Sex, and helped cement his place at the forefront of a new wave of alternative pop.