Young Professor Elvin Gadd
From the Super Mario Wiki
Young Professor Elvin Gadd is a character who appears in the Nintendo DS game, Mario & Luigi: Partners in Time. He is the younger version of Professor Elvin Gadd. Young E. Gadd is encountered in Thwomp Volcano, just before a massive explosion. Mario, Luigi, Baby Mario, and Baby Luigi all find him in his lab at the bottom of the volcano. The reason he was at Thwomp Volcano was to study the behavior of some Thwomps. During the explosion, Young E. Gadd's lab burns down. He later mentions his idea of studying ghosts at the edge of Boo Woods, a reference to Luigi's Mansion.
He looks the same as his "future" counterpart, the only difference being his brown-black hair.