Simplify the following text for a Grade 11 native English-speaking person.
Original: His cumulative performance earned him the inaugural Major League Baseball Rookie of the Year Award ( separate National and American League Rookie of the Year honors were not awarded until 1949 ) .
Simplified: His performance earned him the first Major League Baseball Rookie of the Year Award ( separate National and American League Rookie of the Year honors were not awarded until 1949 ) .