According to Investopedia, a financial controller is the person who is responsible for all the accounting activities in a company. The controller participates in financial accounting, the preparation of taxes, cost accounting and data processing related to corporate accounting and payroll. Controllers are responsible for creating and maintaining the company's accounting system, collecting debts, processing transactions and recording transactions.
About.com notes that a controller is responsible for building and maintaining corporate budgets. A controller may also approve corporate expenditures and oversee a staff. A corporate controller often works directly under a chief financial officer in larger corporations. In smaller companies, the controller may be required to absorb the responsibilities of the CFO. A controller is expected to be able to understand, complete and explain complicated financial transactions. He must also be able to complete periodic financial reports and provide risk management analysis to the company's owner, if necessary.
A controller is expected to be an expert in the use of the company's accounting software, according to About.com. The controller needs at minimum a working knowledge of the technology behind the accounting system and how it works along with knowledge of the company's information technology system as a whole. The controller may be required to assist in the analysis of IT plans and pricing with regard to how the IT needs of the company work within the currently defined budget.