The Hippie or Counter Culture subculture originated in the mid 1960s, in rebellion to modernity and moderation, or as the Hippies put it, to "all repressive hierarchical power structures since these are adverse to the hippie goals of peace, love and freedom." 
Hippies were noted for their liberal stance, including psychedelic music, sexual freedom, drug use (particularly LSD and Marijuana), and rejecting what they saw as the materialistic values of the society around them. The non-violent movement was largely in response to the Vietnam War and used the slogan "peace and love" and "make love not war".
Many of the elements of hippie counterculture, such as an anti-corporate ideology and the anarchic, experimental, libertarian strands, have stayed with hippies as they grew up. Many aspects of alternative lifestyles that were shocking in the 1960s have now become somewhat acceptable in liberal society and amongst those influenced by Hollywood values, such as recreational use of drugs and a loose attitude towards sex. 
Hippies were preceded by the counter-culture beatnik movement of the 1950s.
"Jesus Freaks" were hippies who were born-again Christians and followed Christ's commandments regarding the importance of love and frequently eschewed the use of drugs. Many hippies experimented with alternative living arrangements such as communes, where all work and all possessions were shared.
Examples in Pop Culture
In the movie Easy Rider the protagonists visit a hippie commune in California. Conservative writer Tom Wolfe's account of Ken Kesey's Merry Pranksters in his book The Electric Kool-Aid Acid Test documented one aspect of the hippie scene.
Most famous for writing the novel "One Flew Over the Cuckoo's Nest," Ken Kesey, though a beatnik, was well known for his attributions to the hippie culture. He famously rode around on top of a technicolor school bus called "Furthur." He had a troupe of hippies with whom he lived and traveled, called the Merry Pranksters. The adventures of Kesey and the Pranksters are documented in "The Electric Kool-Aid Acid Test," by Tom Wolfe.
Dr. Timothy Leary (1920 – 1996) was a Harvard professor of psychology. He researched psychedelic drugs, including LSD--and promoted their use. He is best known for coining the phrase "Turn on, tune in, drop out."
Harry Hay was founder of the Radical Faeries, a loosely affiliated international group of mostly gay men, hippies, neopagans, environmentalists, and eco-feminists. Hay is a radical who is accredited as the founder of the modern gay rights movement in the United States. As an octogenarian Hay was still known to dress as a hippie.