Biker
A biker is someone who rides a motorcycle (motorbike). Bikers are sometimes members of a motorcycle club or motorcycle gang.
An outlaw biker - that is, a member of a motorcycle club or motorcycle gang - (stereo)typically rides a Harley-Davidson, grows beards, wears a black helmet without face shields, and wears a leather or denim vest with patches and pins from his own club as well as others. Popular themes for patches are biker parties and meetings, as well as slogans such as "1%", "13", "FTW", and "ACAB". The most well-known bikers are the Hells Angels. Popular biker films are "The Wild One" and "The Wild Angels".
In Germany and Denmark bikers are also known as Rockers. In Australia there is an important distinction between a biker and a bikie: a bikie is a member of a motorcycle gang, while a biker is not.
The biker is also a popular sexual fetish among gay men. As most bikers are rather masculine and wear leather motorcycle clothing they are very attractive to leather fetishists around the world.
Someone riding a bicycle is usually called a cyclist, not a biker.