There are 2 artists named "Happy Birthday":

1) Happy Birthday is Kyle Thomas (aka King Tuff), Chris Weisman, and Ruth Garbus. They formed in November 2008 to play one show at the punk-space “Tinderbox” RIP), in their hometown Brattleboro, Vermont. Kyle needed a band to play his new pop songs because he was too scared to play by himself. They enjoyed playing with each other so much that they decided to keep doing it.

Kyle sings and plays lead guitar. The songs are mostly his, but the band arranges and finishes them together. He is also a painter and drawer and loves top 40, shoes, texting, comic books, etc. Ruth Garbus plays drums and sings. She also makes her own music and art. Chris Weisman plays “inverted-tuning” guitar, bass, and sings. He makes 4-track songs, enjoys reading and writing, and is a guitar teacher.

2) Happy Birthday is a Japanese band consisting of Kisa (songwriter, guitar) and Akko (drums) based in Tokyo, Japan. HAPPY BIRTHDAY formed in February 2010 and signed with Sony Music Associated Records Inc. in 2011.
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Artist biography from last.fm