From Boeing (the company that bought Douglas):
The Douglas A-26/B-26 bomber was the only American bomber to fly missions in three wars. After World War II, it served as a first-line bomber during the Korean War and during the Vietnam War. Douglas started the A-26 in 1941 to follow the A-20/DB-7 Havoc bomber.

Douglas built 2,503 A-26/B-26 Invaders. During production, a number of modifications were progressively introduced so that by 1948, the A-26 was one of the few wartime aircraft types still in service with the post-war U.S. Air Force. When the famous Martin B-26 Marauder retired and the Air Force deleted the designation “A” (for attack category), the Douglas Invader took on the B-26 designation.

Invader versions included the A-26D and A-26E light bombers, GA-26C ground training aircraft and the KA-26A tanker. Some A/B-26s were equipped for photo reconnaissance, and during the 1960s, some surplus B-26s were used to tow targets. The last U.S. military Invader was retired in 1972 and donated to the Smithsonian’s National Air and Space Museum.


For more details on specific models, check below: 
Prototype XA-26 Invader
Prototype XA-26A Invader
A-26B Invader
A-26C Invader
XA-26D Invader
XA-26E Invader
XA-26F Invader
JD-1 Invader
B-26K CounterInvader (A-26A)