You have just enough phlebotinum to resurrect and make immortal any twelve humans who ever lived. The catch is it can’t be yourself or anyone you ever personally knew. So of all the people who could be granted such a boon, who do you think would be the greatest assets to humanity? I’m not sure myself except that I think it would fascinating for some of the hypergenius mathematicians who never met in life to be able to collaborate, like Gauss and Ramanujan.
Are we assuming they never died, as so continued to influence the world from their death up until present day? Or are we bringing them back to life and immortality in the here and now but they’ve missed the years since their death?
I wish I knew enough about science to know who would be valuable in a health/energy/technology sense. Tesla, if the fanboys are to be believed, but that’s almost a stab in the dark.
Martin Luther King, Jr. I wonder what direction civil rights might have taken if his death hadn’t been a violent one, and if he’d lived to steer the movement longer.
John Lennon. Again, his message of peace and antimaterialism was silenced, and then the 80s happened. Might that have been different if he was still a strong public figure? Probably not, but I wonder.
Jesus. Yes or no, man? Just…yes or no?
Mr. Rogers. This has been a really hard week without him.
It’s killing me that I can’t think of any women for the list.
That’s a tough one!
I guess I would pick people who have valuable knowledge, insight, and beliefs. So toss in a few geniuses from varying areas of science, an engineer/physics type, a religious scholar, an artist, … Need to think about this one more.
I was trying to think of a mom type.
And I think the world could benefit from lots more years of Betty White! 
Isaac Asimov is very much missed; he had the knack of explaining science with wondrous clarity.
But…ultimately…no. The question is self-defeating. We need new good people. Asimov, love him as one may, has made room for Stephen Jay Gould, who, in turn, made room for David Quammen, who, in turn, made room for Neil DeGrasse Tyson. The answer isn’t in the past; the answer is in the future. Who will be next?
Trinopus nailed it, besides I don’t hate anyone enough to curse them with immortality.