#3 Brock Lesnar (with Paul Heyman):
Brock Lesnar (with manager Paul Heyman) moved to Smackdown in August 2002 and both remained with the Blue Brand until he left the company in 2004.
While he was a part of Smackdown, Lesnar either reigned as the WWE Champion or remained in the title hunt. While almost all well-established Superstars like Triple H, Shawn Michaels, Goldberg etc. were on Raw and Smackdown's "Big" Superstars like The Undertaker and Kurt Angle were injured, it was Lesnar who carried the Blue Brand for months.
New Champs in WWE! More RIGHT HERE
As discussed above, Heyman moved to Smackdown with Brock Lesnar. Three months later, however, Heyman ended up betraying Lesnar and aligning with Big Show, handing Lesnar his first-ever defeat at Survivor Series 2002.
Heyman's alliance with Big Show was short-lived, however, as Kurt Angle soon became Paul Heyman's client. Heyman became the General Manager of Smackdown by the end of 2003. Although he served as the GM for a few months, many people, even to this day, believe that he was one of the best General Managers of Smackdown.
As much as we would like to see Lesnar returning to the show that made him a star, an appearance by the former Universal Champion is highly unlikely.
He is currently paid on a per-appearance basis by the WWE, and it seems unlikely that the company will want him appearing on an episode of SmackDown, even if it is a special occasion.
Paul Heyman, on the other hand, can appear in a backstage segment with some of SmackDown's other General Managers, such as Paige and Teddy Long. If Brock ends up making a surprise appearance, it would be well-received for sure.