The World

Personality/Appearance
The World (世界 (ザ・ワールド) Za Wārudo) resembles Dio Brando in several ways, having a tall muscular body and the same green heart motifs. It has what seems to be a stopwatch on the back of each hand, symbolizing its power to stop time.

It has never shown any personality, however, in Stone Ocean, it was hinted that if not for Dio's own personality it would go out control.

Powers
The World is similar to Jotaro's Star Platinum with its phenomenal strength, senses and stamina, but also faster and more accurate.

Its defining power is the ability to stop time (possibly in a limited area) allowing only itself and Dio to act. Given Dio's weakened state during Stardust Crusaders, however, this ability only works for a few seconds before time resumes flowing.

He also has at least a measure of Joseph's psychic abilities (specifically, the ability to create a vision on a photograph). A possible explanation for the fact that The World has psychic powers that are only used once is that Hirohiko Araki (the creator of the manga) implied for it to have the power of all of the Stands, or possibly the power of the Stands of the Joestar lineage, due to Dio inhabiting the body of Jonathan Joestar.

It's implied in Part 6 that he wanted to use his Stand to create a perfect world for himself and a handful of subordinates. He enlisted Enrico Pucci as his living "conscience", in case he would go crazy and be "off track".