Wild Card

Wild Card is a series of different main quests

Quick walkthrough
After gaining access to The Tops presidential suite, the following quest will be given:
 * Wild Card: Ace in the Hole

After speaking to Yes Man, three separate quests are given:
 * Wild Card: Change in Management: Find the Platinum Chip, kill/disable House and install the Yes Man into the Lucky 38's mainframe.
 * Wild Card: Side Bets: Make contact with 5 "tribes" (Brotherhood of Steel, White Glove Society, Omertas, Great Khans, Boomers) and decide whether they should be ignored as threats or not.
 * Wild Card: You and What Army?: Go to House's bunker at The Fort and upgrade the securitron army there.

Note: For the "Wild Card" achievement, Wild Card: Finishing Touches will also need to be completed.

Detailed walkthrough
To start the series of quests, talk to Yes Man after confronting Benny at the Tops casino.

Wild Card: Change In Management
Yes Man needs to enter Mr. House's computer network. To do so, one must get the Platinum Chip from Benny, and then kill or disable Mr. House. To disable Mr. House, the Courier must have already entered the Lucky 38 penthouse suite. On the wall to Mr. House's right (Courier's left), there will be a terminal. Activating the terminal will come up with a single option, that is, to open a hidden wall. The new entrance will lead to the antechamber, which leads to an elevator. The elevator is activated by the terminal next to it and takes the player character to Mr. House's control room, where an aged Mr. House resides. Activating the control panel to the left of the walkway gives the player character a choice to open the chamber keeping Mr. House alive. One may then allow Mr. House to live, but allow Yes Man to enter the system, or kill Mr. House and let Yes Man into the system. After dealing with Mr. House, get Yes Man from the Tops casino, where he will instruct the player character to follow him to the Lucky 38. One can then meet him inside the penthouse suite, where he will use the Platinum Chip to enter Mr. House's network.

Wild Card: Side Bets
Yes Man needs to know which "tribes" out in the Mojave will help or hinder him. Specifically, Yes Man wants the player character to meet with and learn about the Brotherhood of Steel, the Omertas, the White Glove Society, the Great Khans, and the Boomers. The Courier must either meet with the groups, learn about their history, and tell Yes Man that they can be ignored, or do multiple quests for each "tribe," putting them into an alliance with them and Yes Man.

Wild Card: You And What Army?
Mr. House's securitron army is in desperate need of an upgrade. With Yes Man in charge, the Securitrons belong to the Courier, so it would be to their best benefit to upgrade their model. Go to Fortification Hill via the Cottonwood Cove ferry (note that if one has the Mark of Caesar the Courier will be granted definite entrance to the Fort). Follow the path up to the top of the hill. One will be led to a drawbridge, which will take the player character to the Fort's camp. From there, head along the left side of the camp. A weather station will be at the end of the left-most camp. Inside are three Praetorian Guards who will attack the player character upon entrance (the one to the right of the entrance might start a quick conversation). Staying in alliance with Caesar will cause them to give the player character their weapons back. Failing the quest Beware the Wrath of Caesar! will cause them to be hostile (this can be avoided by starting the quest Render Unto Caesar). If the latter is true, they will put up a hard fight, even for skilled and high-level player characters, as they all have ballistic fists. Insert the Platinum Chip into the console to the left to open the bunker. Note that there is a small radiation level (1 Rad/sec). Proceed to the end of the bunker and insert the Platinum Chip inside of the console at the end of the bunker. Return to the Lucky 38 to view the newly upgraded Securitrons, as they step up from 9mm rounds and laser shots to missiles and grenades.

Behind the scenes
The term "Wild Card" means either a card that can be anything in poker or a person who is generally unpredictable.