We finally learn how the Red Hulk came to be in this extraordinary issue by writer Jeph Loeb and a large group of excellent artists from Hulk's past and present.
Thaddeus "Thunderbolt" Ross IS the Red Hulk.
The Leader and M.O.D.O.K. offered Ross the chance to kill the Hulk and restore his daughter Betty if he joined them. After accepting, Ross was transformed into the carmine skin monster using the Cathexis Ray Machine built by Doc Samson, which used the gamma power siphoned away from the Hulk in Manhattan by the satellites when he was defeated.
Even with more power than the Hulk's, the Red Hulk (Ross) was unable to kill the real one (Hulk #6) and M.O.D.O.K. lectured him using a Ross L.M.D.
Samson (the evil persona of Leonard), killed Clay Quartermain when he discovered secrets from the Intelligencia plans.
Ross eventually partnered with Banner to defeat the Intelligencia. It was another Ross L.M.D. inside the Redemeer armor, Rulk destroyed.
Now, and at board of the Hellcarrier, the evil doers have won... or so it seemed. Ross turns into the Red Hulk and destroys the Cosmic Hulk, turning more powerful after absorbing the automaton's power. He then absorbs the gamma energy from the Leader, turning him into the ordinary Roger Sterns. Finally, he infiltrates the White House and destroys the Glenn Talbot L.M.D. just as he was on national television, stating to the world that he's in charge now.