Historically Compliance has been viewed as the "business prevention unit", and amongst longer standing members of the finance community, this may still be the case. However, with events such as N2, 9/11, MIFID, the Compliance department is now seen as helping business rather than being a hindrance. The principal function is to interpret regulatory and legal requirements and work with the Business to ensure conformity. A good Compliance officer works with the Business to find solutions, rather than saying "no" automatically. This means that Compliance officers have to be able to understand legal and regulatory requirements and how these can work in practice, acting as a consultant to the Business. As well as understanding internal policy and process, this requires an knowledge of domestic and international rules and regulation that affect business and its operations.
There are in fact many roles in Compliance.There is business facing Compliance (e.g. Equities, Private Banking) who provide specific advice to the Business on their activities. There are other general Compliance functions such as the Money Laundering Reporting Officer, Control Room compliance etc.
Most people have fallen into Compliance (ex regulators, lawyers, accountants) but it is now seen as a career in itself. There are specific business school courses dedicated to Compliance, providing recognised qualifications. Graduates now leave University wanting to be Compliance officers, however most people will have prior experience, e.g. legal. It provides a diverse role that is never the same each day, access to the most senior people in the organisation, and good visibility. Whilst the salaries will never rival those of Investment Bankers they are very good and with a shortage of good officers in the market place, they continue to be driven up.