I think it almost certainly has to be David Karp. This should be an insane and guaranteed payday for him.
Marco Arment hasn't had anything to do with Tumblr in years. He might hold some equity as a result of his time there, especially since he was there at the very beginning, but certainly not more equity than Karp.
Mayer/Yahoo has a long way to go to prove that this was a smart idea. Two years from now they might be the biggest winners, but they're also taking on all the risk at this point.
And as for the investors, this should be a big win for them (although I don't know how much they invested, so hard to say how big of a win), but they are investment firms who have to spread the profits around, opposed to Karp, who is one guy who just got a huge check.
Marco Arment hasn't had anything to do with Tumblr in years. He might hold some equity as a result of his time there, especially since he was there at the very beginning, but certainly not more equity than Karp.
Mayer/Yahoo has a long way to go to prove that this was a smart idea. Two years from now they might be the biggest winners, but they're also taking on all the risk at this point.
And as for the investors, this should be a big win for them (although I don't know how much they invested, so hard to say how big of a win), but they are investment firms who have to spread the profits around, opposed to Karp, who is one guy who just got a huge check.