Judas is mentioned in the synoptic gospels, the Gospel of John and at the beginning of Acts of the Apostles. Mark states that the chief priests were looking for a sly way to arrest Jesus. They decided not to do so during the feast since they were afraid that people would riot; instead, they chose the night before the feast to arrest him. In the Gospel of Luke, Satan enters Judas at this time.
According to the account in the Gospel of John, Judas carried the disciples' money bag. He betrayed Jesus for a bribe of "thirty pieces of silver" by identifying him with a kiss - "the kiss of Judas" - to arresting soldiers of the High Priest Caiaphas, who then turned Jesus over to Pontius Pilate's soldiers.
Judas is still referred to in everyday life and popular culture today. He is referred to in Lady Gaga’s song, Judas. Judas was a traitor, and Gaga is using him as a metaphor for a lover she cannot trust. Yet she can't pull herself away from him -- "I’m just a Holy Fool, oh baby he’s so cruel/But I’m still in love with Judas, baby.” This is fitting because Jesus believed Judas was his friend, someone close to him who he could trust and he later found out that he could not as Gaga suggests she feels with her lover.