What is the oldest satellite still in space?

Could you tell me what the identity of the oldest satellite currently orbiting in space is? Is it still operational or has it been abandoned? How long has it been up there, and what purpose did it originally serve? Are there any plans to decommission it or utilize it for further scientific research? Is it a noteworthy achievement in space exploration, and if so, what makes it stand out from other satellites that have come and gone?