There have been many Captain Americas throughout the years.
Here's a list of Cap's from the regular comic Marvel Universe (that is to say that these are The Canonical Captains) in the order they held the Captian America mantle, not the order they were created:
- Steve Rogers -1st Appearance: 1941 Captain America Comics #1
- Isaiah Bradley -1st Appearance: 2003 Truth: Red, White & Black #1
- William Nasland -1st Appearance: 1977 Invaders #14
- Jeffrey Mace -1st Appearance: 1940 Human Torch Comics #3
- William Burnside -1st Appearance: 1972 (retconned to 1953) Captain America #153
- Bob Russo -1st Appearance: 1974 Captain America #178
- Scar Turpin -1st Appearance: 1974 Captain America #179
- Roscoe Simons -1st Appearance: 1975 Captain America #181
- John Walker -1st Appearance: 1986 Captain America #323
- Sam Wilson -1st Appearance: 1969 Captain America #117 (though events here only retconned in the 1999 Sentinel of Liberty series)
- James Buchanan Barnes -1st Appearance: 1941 Captain America Comics #1 (as Cap in 2008 Captain America vol 5 #34)
- Dave Rickford -1st Appearance: 2011 Captain America #615.1
- Sam Wilson (Sam takes over again in 2014 Captain America vol 7 #25)
For most of these characters things did not turn out too well.
There are also a slue of Alternate Versions of Cap throughout time and the multiverse. Some are characters we know like Scott Summers (AKA Cyclops), while others are somewhat similar like Samantha Wilson from Earth-65 (Where Spider-[Gwen]-Woman comes from). You can see a list of them here: Alt-Vers Caps
In Films and Television however Grant Gardner was the only OTHER person, aside from Steve Rogers, revealed to be Captain America.