Story Identification: Human taught powers by aliens and tries to save the universe

Question

I read a sci fi book about 12-13 years ago and I think it was fairly new at the time, I would like to find it again but I can't for the life of me remember the title or the author. Trying to google the the story of the book doesn't get me much either. From what I remember this is the basic premise of the book

• The hero is an ex soldier who has been taught some sort of powers by a race of aliens
• Said race of aliens have disappeared, possibly ascended to a higher state of existence. Except for the alien that taught the hero in the first place
• Humans and the aliens might have been allies at some stage
• Some mysterious force is threatening the universe and it's something like an ancient enemy of the alien race
• The hero has some sort of stone or device left behind by the alien race that allows him to develop his powers by meditating

That's all I have. It has I remember it as being quite action packed as well. I know it's very vague but if it rings a bell with anyone I'd be delighted.

Edited 05/05 While Zimul8r's answer of the Lensman series ticks all the boxes as far as the plot points I can remember, it is not the book I'm looking for. I think this was a standalone book as far as I can remember. Oh, and because I was reading mainly fantasy novels at the time there's quite a high likelihood that I picked this up because I recognized the author from some fantasy novel.

Answer 1

After scrolling through almost all damned science fiction books on Amazon I finally found it :-)

The Great War with the vile Al'ar was all but forgotten, the last alien resistance eliminated ten years ago. However, war hero Joshua Wolfe cannot forget. Friend, prisoner then destroyer of the Al'ar, they called him Shadow Warrior - master of the Al'ar killing arts. He alone knew the conflict was far from over.

Shadow Warrior by Chris Bunch

http://www.amazon.co.uk/gp/aw/d/B0043VDILK?ie=UTF8&redirectFromSS=1&pc_redir=T1&noEncodingTag=1&robot_redir=1

Answer 2

I'm gonna go with E. E. "Doc" Smith's Lensman Series (1948-1954)

The hero is an ex soldier who has been taught some sort of powers by a race of aliens

Virgil Samms, the head of the Triplanetary Service (a military org) is contacted by the Arisians, an advanced alien race, who offer him the tools he'll need to build the Galactic Partol needed to stabilize the galaxy.

Said race of aliens have disappeared, possibly ascended to a higher state of existence. Except for the alien that taught the hero in the first place

The Arisians have evolved to beings of pure intellect, and the humans only ever deal with one of them. In the end, the Arisians remove themselves from our plane of existence, leaving the Lensmen to defend it.

Humans and the aliens might have been allies at some stage

The Arisians work in secret on Earth for generations trying to breed a species capable of defeating their enemies. they later provide the Lens' and train the Lensmen.

Some mysterious force is threatening the universe and it's something like an ancient enemy of the alien race

The Eddorians, a ruthless and power hungry race from another space-time continuum, are looking to dominate our galaxy. The Arisians deteced them first, and managed to remain undetected while the worked on their breeding program.

The hero has some sort of stone or device left behind by the alien race that allows him to develop his powers by meditating

The Lens, a large gem-like device worn on the wrist, gives it's owner mental powers, which the Lensmen train to develop over time.