A comptroller is a senior official who watches the money — what comes in, what goes out, and whether the accounts are straight. You see the title on the doors of government offices and some large organisations. Though actually, this is the same job as a controller. For a long time the two spellings were just two ways to write one word, and people said them the same way. The extra letters crept in because people thought the word came from a French word for 'account.' That was a tidy story about the spelling, not the true history. Later, some speakers began to pronounce the mp because they could see it written. In everyday English, people mostly say controller; comptroller is the old official title. It is a very formal word.