Fiennes told the Radio Times that he wanted to portray the character in a slightly unusual way.
"I wanted to get away from that iconic look of a wizard with the pointy hat and staff and long beard," he said.
"I think of him as a mix between Obi-Wan Kenobi and Donald Rumsfeld. This sort of great, machiavellian puppet master behind the scenes, who takes this young boy - Arthur - and grooms him for power. Theirs is like an Obi-Wan and Luke Skywalker relationship."
Fiennes also suggested that he didn't want to focus too much on Merlin as a wizard.
"I felt I could get more of a handle on him as a great political manipulator," he said. "For him, magic is like abusing a class-A drug - not that I've done that - it can take over and begins to control and condemn you. This is a young Merlin and he's exploring those powers, learning to understand them. He's developing into the Merlin that we know."
Fiennes has previously admitted that he was initially unsure about taking on a role in Camelot but has described each of the episodes as a "mini film".
Camelot begins on Saturday at 9pm on Channel 4.