Massive Attack is an English trip hop collective formed in 1988 in Bristol by Robert Del Naja, Grant Marshall, Adrian Thaws and Andrew Vowles. Now a duo of Del Naja and Marshall, the group released their influential debut Blue Lines in 1991, widely regarded as the first trip hop album. Their acclaimed track "Unfinished Sympathy" and later hits like "Teardrop" brought international recognition, with the latter featured as the theme for the television series House. Albums such as Blue Lines and Mezzanine are considered classics and have appeared on major greatest albums lists. Massive Attack is known for their atmospheric sound, collaborations with vocalists like Horace Andy, Shara Nelson, Elizabeth Fraser and Sinéad O'Connor, and for their commitment to political and environmental causes. They have won awards including a Brit Award and MTV Europe Music Awards, and have sold over 13 million albums worldwide.