Presidential pardons have always been controversial, from the first pardon of the Whiskey Rebels to Gerald Ford's heated pardon of former President Richard Nixon after one of the most infamous scandals in our nation's history.

Slideshow: Presidential Pardons

A pardon is the forgiveness of a crime and the consequences associated with it. The Constitution grants the current president the power to forgive federal offenses.

Pardons begin by way of petition and are addressed to the president, who grants or denies the request. If the request is granted, the pardon can either clear all penalties, require the petitioner to submit to conditions in order to receive full pardon, or commute a sentence.

The first generation of Americans was very skeptical of maintaining pardons after the colonies gained their independence. Pardons had been widely abused in Europe, and they feared the same abuse in the new nation.

Whiskey Rebels

George Washington issued the first pardon to a group known as the Whiskey Rebels. After the Revolutionary War, the federal government assumed debt from the states and sought to pay off the deficit with a tax on distilled spirits. The tax was fiercely opposed with protests -- some violent -- until finally culminating in a multi-state armed rebellion in 1794. The federal government responded by summoning local militias to respond, marking the first time the federal government used military force to maintain authority over its people and setting a precedent so that citizens who wished to change laws would have to do so peacefully via constitutional means.

The whiskey taxes were repealed in 1803, having been largely unenforceable and unsuccessful. Washington granted pardons to those who had been convicted or indicted of treason, which otherwise would have resulted in death by hanging.

'Character' Pardons

On a smaller scale, President Abraham Lincoln issued two pardons based solely on the man in question's character.

Arthur O'Bryan was convicted of attempted bestiality, but was pardoned by Lincoln because he felt O'Bryan was "otherwise reputable."

Lincoln also pardoned John Lawson for his "reputation for honesty." Lawson had been convicted of counterfeiting.

Confederate Citizens

President Andrew Johnson took office after Lincoln's assassination and took charge of the Reconstruction after the Civil War. When Congress was not in session, Johnson pardoned most confederate citizens on the condition that they swore allegiance to the Union. Johnson did not immediately pardon former Confederate officials, those who fought on the side of the rebels or wealthy individuals who provided funding. Instead, they had to petition individually. Johnson's actions while Congress was out of session made him unpopular and he became the first president to have been impeached.

Jimmy Hoffa

Jimmy Hoffa was president of the Teamsters union and made no attempts to conceal his connections to the mafia and organized crime, instead using his connections to intimidate his opponents. He was involved in a number of federal investigations in the 1950s and 60s, and was finally convicted of jury tampering and fraud in 1964.

Still, Hoffa retained the support of most union members. Supreme Court Justice Earl Warren later called Hoffa's conviction an "affront to the quality and fairness of federal law enforcement."

Nixon pardoned Hoffa on the sole condition that he would not engage directly or indirectly in the management of a labor union until at least 1980. Hoffa, who had refused to renounce his title of president, eventually agreed to the terms and was released in 1971.

Hoffa disappeared in 1975. He was supposed to meet a known mafia mobster and a Teamsters boss for lunch at the Machus Red Fox restaurant in Michigan, and had told his wife he would be home in time for dinner. Investigators believe he may have been trying to resume control of the Teamsters when he disappeared.

Hoffa was declared legally dead in 1983, but his body has never been found. His disappearance remains one of the most infamous murders in our nation's history.

President Nixon

Nixon himself was pardoned for his involvement in the Watergate scandals, which began when the Democratic National Committee headquarters at the Watergate hotel complex was broken into in 1972.

Investigations revealed that the burglary was carried out by some of Nixon's staff, and also connected the president to a large number of crimes and abuses ranging from political sabotage to illegal wiretapping.

In the face of an imminent impeachment and conviction, Nixon resigned, making him the only president in history to do so. His successor, Ford, issued an extremely controversial pardon for any federal crimes Nixon may have committed while in office. The pardon was extremely unpopular, and many believe it was a contributing factor in Ford losing the following election.

Vietnam Draft Dodgers

One of President Jimmy Carter's first actions after he took office was to issue an unconditional pardon to those who had evaded the Vietnam draft. Ford had earlier issued a plan for conditional amnesty, but Carter hoped to remove conditions in order to heal the nation's wounds.

Carter's pardon was not all-encompassing, however, and applied only to civilians who had fled or failed to register. It did not apply to the soldiers who went AWOL or had dishonorable discharges.

The pardon was popular with amnesty groups, but enraged veterans. Critics argued that the pardon would only encourage more people to avoid service, and that the pardon was disrespectful to those soldiers who had fought and died.

Deep Throat

Code name Deep Throat was a large player in uncovering the Watergate scandals by serving details of Nixon's involvement to the press. Although there were hints and suspicions at his identity, Deep Throat remained an anonymous informant for over 30 years.

In 2005, FBI veteran Mark Felt admitted that he was the whistle blowing Deep Throat. Felt was found guilty in 1978 of overstepping warrants and searching the homes of Vietnam protestors.

President Ronald Reagan overstepped the Justice Department and pardoned Felt in the middle of his appeals. Reagan said he believed that since America had generously pardoned draft dodgers for refusing to serve their country, the country should also extend the courtesy to those who had acted in an attempt to keep the country safe from terrorism during a time of war.

Iran-Contra

The Reagan administration was dedicated to quelling the spread of Communism, and the Nicaraguan Contras combating the Cuban-backed Sandinistas received assistance from the government in the form of financial funding and CIA training.

The combination of the words "Iran" and "Contra" into one unpopular affair occurred after several complex, covert actions carried out in the name of democracy were uncovered.

Iran requested to purchase weapons from the United States in 1985 for use in its war against Iraq. Former National Security Adviser Robert McFarlane advised Reagan that supplying Iran with weapons could improve U.S. relations in the Middle East, despite the fact that there was an embargo that explicitly forbade selling arms to Iran.

However, Iranian terrorists were holding seven American hostages and spurred a divisive arms-for-hostages proposal that divided Reagan's administration.

By the time the deal was discovered, over 1,500 missiles had been shipped to Iran and only three hostages had been released -- only to be replaced by three additional hostages.

The deal was exposed by a Lebanese newspaper. Reagan originally denied the arms-for-hostages trade, but later admitted it a week later and defended the actions on the basis of their good intentions.

During probes regarding the arms-for-hostages deal, investigators discovered a huge discrepancy in financing. Only $12 million of the $30 million Iranian weapons invoice had been received because the funds had been diverted to fund the Contras by Lt. Col. Oliver North of the National Security Council.

Speculation of the depth of the Reagan administration's involvement ran rampant; although there was never sufficient evidence to link Reagan himself to the diversion of funds. In the end, 14 people were charged in connection with the Iran-Contra affair.

Once Former President George H.W. Bush took office, he issued pardons for those involved and halted the legal proceedings against members of the Reagan administration. In doing so, Bush also saved himself from having to testify.

Eleventh Hour

On the last day of Bill Clinton's presidency, he issued over 100 pardons -- some of which were extremely controversial.

Although Carter had already commuted her sentence and released her from jail, Clinton issued a full pardon for Patty Hearst, daughter of American publishing tycoon William Randolph Hearst. Patty had been arrested for her involvement in an armed robbery of a San Francisco bank after she was kidnapped by an urban guerilla group known as the Symbionese Liberation Army. Hearst's defense claimed she had been brainwashed and abused by the group.

Clinton also pardoned 12 convicted FALN terrorists -- members of the Puerto Rican nationalist group Armed Forces of National Liberation -- who carried out 150 bombings within the United States.

Perhaps the most controversial of Clinton's pardons was that given to exiled financier Marc Rich who had been indicted for evading more than $48 million in taxes and for conducting illegal oil deals during the hostage crisis.

The pardon enraged many and prompted an investigation into whether the pardon had been bought. Rich's ex-wife had donated largely to the Clintons and the Democrats. In the end, there was never enough evidence to convict.

However, in 2007, Clinton's pardons resurfaced again when three of the recipients donated to his wife's presidential campaign. While this is not illegal, it certainly helped rekindle suspicions.

Lewis 'Scooter' Libby

The most recent pardon that garnered unpopular attention was when President George W. Bush commuted the sentence of Lewis "Scooter" Libby after the Plamegate scandal.

Libby, former Chief of Staff to Vice President Dick Cheney, was sentenced to 30 months in prison for perjury, obstruction of justice and lying to investigators probing the 2003 exposure of the name of CIA operative Valerie Plame.

Plame's husband, former Ambassador Joseph C. Wilson, stated in various interviews and subsequent writings that members of the Bush administration leaked his wife's identity in retaliation to an article he wrote claiming that the administration had misrepresented intelligence from his report to suggest that Iraq was seeking uranium and weapons of mass destruction. Plame's name was leaked eight days after the article appeared.

Several Bush administration officials were subpoenaed, and the press hovered over the case. In the end, Bush commuted Libby's sentence although the fine, probation, and felony conviction still remain.

Pardons still come under intense scrutiny, and the number of pardons issued varies widely by administration.