Christ himself is, of course, THE intercessor of all men. He died for us so that we might live. But as Thomas à Kempis put it in The Imitation of Christ, we are called to be "little Christs," and this means, as much as we can, doing for others what Christ did for us.
The catechism explains further:
2634 Intercession is a prayer of petition which leads us to pray as Jesus did. He is the one intercessor with the Father on behalf of all men, especially sinners. He is "able for all time to save those who draw near to God through him, since he always lives to make intercession for them." The Holy Spirit "himself intercedes for us . . . and intercedes for the saints according to the will of God."
2635 Since Abraham, intercession - asking on behalf of another has been characteristic of a heart attuned to God's mercy. In the age of the Church, Christian intercession participates in Christ's, as an expression of the communion of saints. In intercession, he who prays looks "not only to his own interests, but also to the interests of others," even to the point of praying for those who do him harm.
2636 The first Christian communities lived this form of fellowship intensely. Thus the Apostle Paul gives them a share in his ministry of preaching the Gospel but also intercedes for them. The intercession of Christians recognizes no boundaries: "for all men, for kings and all who are in high positions," for persecutors, for the salvation of those who reject the Gospel.
Catholics also believe that this call extends even beyond the grave, and that those Christians who have died and gone to Heaven continue to intercede for those on Earth. Let us be imitators of Christ, and continually lift each other up in prayer!
But I say to you, love your enemies, and pray for those who persecute you (Matt 5:44)
In the same way, the Spirit too comes to the aid of our weakness; for we do not know how to pray as we ought, but the Spirit itself intercedes with inexpressible groanings. And the one who searches hearts knows what is the intention of the Spirit, because it intercedes for the holy ones according to God's will. (Rom 8:26-7)
It is Christ (Jesus) who died, rather, was raised, who also is at the right hand of God, who indeed intercedes for us. (Rom 8:34)
[Christ] is always able to save those who approach God through him, since he lives forever to make intercession for them. (Hebrews 7:25)
Bear one another's burdens, and so you will fulfill the law of Christ. (Gal 6:2)
Do nothing out of selfishness or out of vainglory; rather, humbly regard others as more important than yourselves, each looking out not for his own interests, but (also) everyone for those of others. (Phil 2:3-4)
As they were stoning Stephen, he called out, "Lord Jesus, receive my spirit." Then he fell to his knees and cried out in a loud voice, "Lord, do not hold this sin against them"; and when he said this, he fell asleep. (Acts 7:60)
Peter thus was being kept in prison, but prayer by the church was fervently being made to God on his behalf. (Acts 12:5)
With all prayer and supplication, pray at every opportunity in the Spirit. To that end, be watchful with all perseverance and supplication for all the holy ones and also for me, that speech may be given me to open my mouth, to make known with boldness the mystery of the gospel for which I am an ambassador in chains, so that I may have the courage to speak as I must. (Eph 6:18-20)
Brothers, pray for us (too). (1 Thess 5:25)
To this end, we always pray for you, that our God may make you worthy of his calling and powerfully bring to fulfillment every good purpose and every effort of faith, that the name of our Lord Jesus may be glorified in you, and you in him, in accord with the grace of our God and Lord Jesus Christ. (2 Thess 1:11-12)
First of all, then, I ask that supplications, prayers, petitions, and thanksgivings be offered for everyone, for kings and for all in authority, that we may lead a quiet and tranquil life in all devotion and dignity. (1 Tim 2:1-2)