A word to describe someone who acts contrary to self-interest?

Is "altruist" the word you're looking for?

I have read literature on "self-sabotage" or "self-saboteurs", for people who sabotage their own efforts or ruin their own chances. There is another word-"imposter"-whch is used in organizational or psych literature to mean someone who does not feel like they really belong in their position, as if they didn't deserve or earn it.

The single word may be 'self-abnegation' which means denial or invalidation of one's own needs, interest etc. in the sake of another's; the setting aside of self interest.

'Akrasia' suggested in the question actully means lack of self control or intemperance.

Akrasia is, in fact, a reasonable word to describe self-defeating behavior, as it approaches a central interpretation self-interest:

noun

[MASS NOUN] chiefly Philosophy
The state of mind in which someone acts against their better judgement through weakness of will.
_ODO

Akrasia applies appropriately because our better judgment is generally more consistent with our real self-interest, but the word actually denotes a lack of moral power that inhibits our better judgment:

Origin

Early 19th century: from Greek, from a- 'without' + kratos 'power, strength'. The term is used especially with reference to Aristotle's Nicomachean Ethics.
_ODO

Aristotle discussed akrasia (translated incontinence by W. D. Ross) in Book VII of Nicomachean Ethics:

Let us now make a fresh beginning and point out that of moral states to be avoided there are three kinds-vice, incontinence, brutishness ...
while we have discussed vice before we must now discuss incontinence and softness (or effeminacy) ...
the incontinent man, knowing that what he does is bad, does it as a result of passion ...
Now we may ask (1) how a man who judges rightly can behave incontinently ...
the continent man abides by his resolutions more and the incontinent man less than most men can.
_{Emphasis added}

As an external pattern of behavior that reveals an internal ethical ambivalence--the inability to do what one knows is better, or refrain from what one knows is worse--akrasia manifests in self-defeating and self-destructive behavior.

For example, an overwhelming cultural warning against the destructive nature of smoking cigarettes has prevailed with explicit scientific evidence and implicit emotional manipulation for an entire generation. If we find a child or even a teen smoking cigarettes, we recognize the ignorance at the root of their choice. Against our better judgment, we adults may legitimately enjoy the fleeting pleasures of our established habit with no remorse, but for most of us, it remains an akratic addiction: every puff immediately reduces the physiological capacity of our hearts and lungs, consequentially inhibits the strength of our minds and bodies, and ultimately diminishes our life expectancy, but we haven't the power to stop.