who the most successful photo journalist and what mad them successful?

Answer 1

It was Joe Rosenthal, he took the picture of the flag raising on Iwo Jima.
He was lucky to be in the right place at the right time.

Answer 2

Paperclip is wrong, that photo of the raising the US flag at Iro Jima was a staged event taken about a half hour after the original flag was raised.
There have been a number of photos that have been rated much better -- The photo of a Spanish Republican soldier during the Spanish Civil War being killed is more famous and the photo was taken by Robert Capa.
A photo taken in Papua New Guinea during WW-2 of a "Fuzzy Wuzzy Angle (a PNG native) leading a blinded Australian Soldier is also famous. That was taken by George Silk.
Cinema news footage taken in Papua New Guinea during WW-2 of one Australian soldier helping another Australian Soldier with bandages across his eyes, while crossing a river is another. That was taken by Damian Parer.
Another lot of footage, also by Damian Parer, was taken of the bombing and straffing of Japanese ships during the 'Battle of the Bismark Sea". The film and photos were taken from behind the pilot.
The photo taken of the South Vietnamese Police General killing a suspected NLF (Viet Cong) during TET 1968 is another famous photo. I have forgotten who took that. There is also TV footage taken at the same time by Neil Davis who worked for Visnews, a British based TV news syndication service.
The young Vietnamese girl running down the road after a US bombing strike on her village with napalm is another memorable vision. I forget who shot the famous shot, but believe it was an AP photographer. There were several TV camera crews there and Thames TV are accredited with the famous footage, but I believe it was American ABC footage that really had the impact.
There are others that do not include war, although most people remember them.