Dragon's Den investors usually request equity, meaning an ownership stake in the entrepreneur's company, in exchange for their money. A pitch normally states the amount sought and the percentage of the business offered.
Equity gives the investor a claim on part of the company and its future value. Negotiations can change the percentage, involve more than one dragon or end without a deal if the valuation or terms are unacceptable.
Rent, a salary and a patent are different concepts. Rent is payment for using property, a salary compensates an employee and a patent protects an invention; none is the standard ownership currency negotiated in the Den.