I had this book during the 1980s and early 1990s, so it could be from the 1970s as well. It's a hard back book with several linked stories in it, mainly following one protagonist and his sidekick (one or other of the two may have been called "Walker").
The book was heavily illustrated in the same style as John Berkey and others of the era, with full page full colour illustrations sitting alongside story pages, and almost certainly involved illustrations intended for other uses being used to illustrate this book (the illustrations rarely directly matched the events of the story).
The ending of the book involved a final battle between the protagonist and an alien invasion fleet, resulting in the protagonist being sucked through a wormhole or other spacial distortion with the enemy flagship, seemingly never to be heard of again.
His side kick is telling these seemingly tall stories in a bar at the end of the book, many years later, very sad that he lost his friend. And then who should just walk through the door...
The book cover was reddish brown in colour, with an illustration of a spaceship (of course).
The Terran Trade Authority books are extremely similar in style, but do not match my recollection of this book as they are not story based, and the covers do not match what I recall.