Who won last year's college football championship?
The Alabama Crimson Tide and Georgia Bulldogs played in the 2018 College Football Playoff National Championship. Alabama defeated Georgia in overtime 26–23.
Who won the 2017 College Football Championship?
Alabama
2017 NCAA Division I FBS football season
The Alabama Crimson Tide and Georgia Bulldogs played in the 2018 College Football Playoff National Championship. Alabama defeated Georgia in overtime 26–23.
Who won the 2016 College Football Championship?
Alabama
2017 NCAA Division I FBS football season
The Ohio State Buckeyes won the game, 42–20, marking the first national championship awarded under the CFP system. Following the game, the AP Poll and Coaches' Poll also named Ohio State as their top team of the season, marking Ohio State's first national championship since 2002 and their 8th overall.
Who won the 2015 College Football Championship?
Ohio State
2015 College Football Playoff National Championship
2020 College Football Playoff National Championship
https://en.wikipedia.org/wiki/2020%20College%20Football%20Playoff%20National%20Championship
2016 College Football Playoff National Championship
https://en.wikipedia.org/wiki/2016%20College%20Football%20Playoff%20National%20Championship
2017 NCAA Division I FBS football season
https://en.wikipedia.org/wiki/2017%20NCAA%20Division%20I%20FBS%20football%20season
2015 College Football Playoff National Championship
https://en.wikipedia.org/wiki/2015%20College%20Football%20Playoff%20National%20Championship
The Ohio State Buckeyes won the game, 42–20, marking the first national championship awarded under the CFP system. 
2015 College Football Playoff National Championship
The game was played between the winners of two designated semi-final bowl games played on January 1, 2015: the No. 4 Ohio State Buckeyes, who upset No. 1 Alabama 42–35 in the 2015 Sugar Bowl, and the No. 2 Oregon Ducks, who defeated previously unbeaten No. 3 Florida State 59–20 in the 2015 Rose Bowl.
2015 College Football Playoff National Championship
The game was played between the winners of two pre-designated semifinal bowls played on December 31, 2015: the No. 1 Clemson Tigers, who beat the No. 4 Oklahoma Sooners 37–17 at the Orange Bowl, coached by Dabo Swinney in his 8th season, and the No. 2 Alabama Crimson Tide, who shut out the No. 3 Michigan State Spartans 38–0 at the Cotton Bowl Classic
2016 College Football Playoff National Championship
The 13–1 Alabama Crimson Tide won the game, holding off the undefeated Clemson Tigers 45–40 in the fourth quarter. 
2016 College Football Playoff National Championship
The Alabama Crimson Tide defeated the Georgia Bulldogs 26–23, coming back from a 13–0 deficit at halftime to secure the win in overtime.
2018 College Football Playoff National Championship
The Ohio State Buckeyes beat the Oregon Ducks, 42-20, in the 2015 College Football Championship game, marking the first national championship awarded under the CFP system. The Alabama Crimson Tide beat the Clemson Tigers, 45-40, to win the 2016 College Football Championship game. The Aabama Crimson Tide beat the Georgia Bulldogs, 26-23, to win the 2018 College Football Championship game, that decided the winner of the 2017 season.