MCU: 10 Marvel Movie Characters Who've Changed The Most
9. Rhodey

When he was first introduced, Colonel James Rhodes was an excellent military leader, having flown 138 combat missions and a scornful friend of Tony Stark, offering a moralising grounding point to the playboy and trying to keep him on the straight and narrow. He was the archetypical good guy side-kick, in other words.
He had aspirations to become War Machine, but it was an unrequited love initially, as he wasn't allowed to play.
Almost since he took over the suit (and suddenly started looking like Don Cheadle), he's gone through some serious changes, almost shifting to become more like the cocky show-off Stark was as Stark has become more vulnerable and weird. He's now more like emotive comic relief, and while he was a full-blown Avenger, it didn't last and he's now permanently paralysed after Civil War.
What Caused The Changes?
It looks like Stark moving away from his arrogant, destructive playboy image meant Rhodey had to change too, and like his access to the War Machine armour led him back to a sort of cocky Top Gun-style machismo.
As for the physical change in Civil War, being shot by an Infinity Stone and dropped out of the air tends to have that sort of effect.