Dr. Brain is a series of educational games made by Sierra On-Line in the 1990s. The objective of each game is solving a series of puzzles in order to proceed further into the game. The series was later picked up by Knowledge Adventure who turned it into a more action-oriented game.
The original two games were created by an in-house team at Sierra. After the second game was released, Sierra acquired another company, Bright Star Technology, known for its educational games. The series was turned over to a Bright Star team, explaining the change in direction from the second game to the third.
Dr. Brain is an elderly absentminded professor. The first two Sierra games follow the Dr. Thaddeus Egghead Brain, and the last two follow Dr. Thaddeaus Puzzle Brain the Third. Dr. Brain was 'reincarnated' as Dr. Cranium in Quest for Glory IV (both Dr. Brain and Quest for Glory series are designed by Corey Cole, though Dr. Cranium mentions once that one of his descendants would get "his very own game".). The background information for Dr. Cranium in the Shadows of Darkness Hintbook written by Lori and Corey Cole states that Dr. T. Egghead Brain is Dr. Cranium's great-great grandson.
Source: Wikipedia, "Dr. Brain", available under the CC-BY-SA License.