Final answer:
Glenn T. Seaborg was the last person to make a difference to how the periodic table looks.
Step-by-step explanation:
The last person to make a difference to how the periodic table looks was Glenn T. Seaborg. Seaborg was an American chemist who discovered many transuranium elements and played a key role in expanding the periodic table by adding new elements to it. He also proposed changes to the layout and organization of the periodic table, including the placement of the actinides and lanthanides.