The Sentry known as Robert Reynolds first appeared in his self-titled Marvel Knights limited series in Sep 2000, in which he was marketed as a 'forgotten' creation of Stan Lee, but this itself was a fiction created as a marketing ploy. The fictional history of the Sentry, written by different writers in various publications, tends to be self-contradictory, as much of it comes from the Sentry himself, an unreliable narrator suffering from delusions symptomatic of severe mental illness. Since his dubious introduction, the Sentry's history has been 'retconned' (retroactive continuity) into the Marvel Universe proper's history via the convenience of some kind of cataclysmic event, from which all recollection of the Sentry had been removed from everyone's memory (including his own). While the Sentry gets his power from a serum that is multiple times more powerful than Captain America's, it is also possible he is a refugee life-force from another universe which just accommodates the serum. Regardless of the exact details of his origin, the Sentry possesses such immense strength, speed, and invulnerability, that he is clearly in the top tier of power classes. He may even be the most powerful superhero in the Marvel Universe, as he has been observed emitting light, teleporting, implanting his memories in another's mind, using his mental power to hold his form together, and even recreating himself after bodily destruction. In general, the Sentry has not been received 'seriously' into the Marvel Universe. The absurdities surrounding his introduction and his insane power levels make him a stock character at most, if not outright ignored.