LVIV, Ukraine — When diplomats from Russia and Ukraine met for talks within the Nineteenth-century Dolmabahce Palace in Istanbul on Tuesday, their host urged the antagonists to succeed in a cease-fire “to the advantage of everybody.”

These phrases from President Recep Tayyip Erdogan of Turkey could have resonated particularly with a Russian oligarch within the room, mysteriously watching from a front-row seat.

The oligarch, Roman Abramovich, the 55-year-old proprietor of Britain’s storied Chelsea Soccer Membership soccer workforce, shouldn’t be a member of the Russian facet of the talks. He has been sanctioned by the British authorities — however, curiously, not the USA — for ties with President Vladimir V. Putin of Russia, who began the battle.

Britain’s overseas secretary, Liz Truss, has stated that oligarchs like Mr. Abramovich ought to “grasp their heads in disgrace.” Ukraine’s ambassador to Britain, Vadym Prystaiko, informed the BBC that he had “no concept what Mr. Abramovich is claiming or doing” on the talks. Dmitri S. Peskov, the Kremlin spokesman, wouldn’t specify what Mr. Abramovich was doing however stated Moscow had “permitted” his participation to coordinate between either side.

The unknowns of why he was within the room solely added intrigue to the talks, which have been reported to have made the primary important progress because the battle started greater than a month in the past. And in an additional trace of thriller, information emerged that Mr. Abramovich had been entangled in a weird episode, earlier this month, regarding whether or not he and members of the Ukrainian negotiating workforce have been poisoned.

The oligarch, who didn’t touch upon why he was attending the talks, seemed to be attempting to current himself to the world as an earnest and trusted conduit between Kyiv and Moscow. Critics of Mr. Abramovich urged he was grandstanding for publicity, a part of an effort to save lots of his empire.

Nonetheless, Mr. Abramovich has gotten near a key member of Ukraine’s negotiating workforce, Rustem Umerov, in keeping with an individual acquainted with the talks, who spoke on situation of anonymity as a result of the negotiations are delicate. Mr. Umerov, this particular person stated, believes that Mr. Abramovich desires to see the battle stopped.

By the point Mr. Abramovich had been sanctioned by the British authorities, he had been taking part in a quiet function within the peace course of. He was acknowledged as a part of a public spherical of negotiations in Belarus that started 4 days into the battle. However now reviews have emerged of Mr. Abramovich’s participation in a much less publicized monitor, mediated by Turkey, which had him shuttling between Kyiv, Moscow and Istanbul.

His function included personally delivering a handwritten letter by President Volodomyr Zelensky of Ukraine addressing a top level view of his phrases for an settlement to Mr. Putin, in keeping with a report from The Sunday Occasions.

Of all of the wealthy businessmen across the Russian president, Mr. Abramovich, a Russian-Portuguese-Israeli multibillionaire, stands alone in his potential to mix each a popularity for high-level Kremlin connections and a celeb profile — if not standing and acceptance — within the capitals of the West.

Mr. Abramovich began working in enterprise within the late Eighties, shopping for and promoting dolls, candies, cigarettes, and extra. He started to amass his fortune within the mid-Nineteen Nineties, after the collapse of the Soviet Union, when he and a enterprise companion persuaded the Russian authorities to promote them the state-run oil firm Sibneft for about $200 million. In 2005, whereas he was serving because the governor of Russia’s resource-rich northeastern province of Chukotka, he bought his stake again to the federal government for $11.9 billion.

As Mr. Putin introduced businessmen to heel by jailing and intimidating them, Mr. Abramovich was among the many billionaires who managed to stay on good phrases with the Kremlin. He used his wealth to purchase luxurious properties in New York, London, Tel Aviv, St. Barts and Aspen, Colorado, in addition to two superyachts, a number of Ferrari, Porsche and Aston Martin sports activities vehicles, and a personal Boeing 787 Dreamliner jet — now grounded due to the sanctions on him.

He has additionally extensively funded the Moscow artwork scene, together with as co-founder of the Storage Middle for Modern Artwork in Moscow, and performed a task on the board of the famed Bolshoi Theater.

Final yr, his web price was estimated by Forbes at $14.5 billion, making him considered one of Israel’s richest residents and the eleventh richest Russian. A lot of it could have evaporated due to the onerous sanctions. Britain has imposed such tight restrictions on Mr. Abramovich’s Chelsea membership that some say they quantity to authorities management.

On the eve of the Ukraine-Russia discussions in Istanbul, reviews emerged in The Wall Road Journal and in Bellingcat, an investigative journalism group, that Mr. Abramovich, Mr. Umerov and one other Russian businessman had suffered signs related to poisoning between the night time of March 3 and the morning of March 4 after a spherical of consultations.

In accordance with Bellingcat, the individuals all drank solely water and ate chocolate. Negotiations went till 10 p.m. that night time in Kyiv, and in a single day the boys started experiencing the signs, together with impaired imaginative and prescient and peeling pores and skin.

As they drove from Kyiv to the western Ukrainian metropolis of Lviv — en route, through Poland, to the subsequent spherical of negotiations in Turkey — the workforce enlisted the assistance of Bellingcat’s government director, Christo Grozev, who had extensively researched the poisoning of the Russian opposition politician, Aleksei A. Navalny.

The signs have been extreme sufficient that Mr. Abramovich requested the scientist analyzing him, “Are we dying?” one one who was current informed The New York Occasions.

The consultants who examined the boys stated “the dosage and kind of toxin used was doubtless inadequate to trigger life-threatening injury, and most definitely was supposed to scare the victims versus trigger everlasting injury,” in keeping with a sequence of Twitter postings from Bellingcat. “The victims stated they weren’t conscious of who may need had an curiosity in an assault,” they stated.

Some Western officers sought to tamp down considerations over doable poisoning, suggesting that “environmental elements” have been accountable.

“The proof is reasonably sketchy and in a tough place,” one Western official stated.

Mr. Peskov, the Kremlin spokesman, stated Tuesday that the reviews of poisoning have been a part of an “data battle.”

Moreover the British sanctions on him, Mr. Abramovich additionally has come below European Union and Canadian sanctions. Reviews have emerged of Mr. Zelensky asking President Biden to chorus from sanctioning Mr. Abramovich due to the function he has been taking part in.

“This can be a mixed operation — to assist him and to assist the Kremlin,” stated Ksenia Svetlova, a Moscow-born Israeli political analyst, former lawmaker, and skilled on the Russian Israeli group.

“Moscow thinks they will use him,” she stated, “and the West additionally thinks they will use him.”

The truth that he isn’t a part of Russia’s official delegation, she stated, gave him extra leeway to succeed in a compromise.

“It’s the story of fine cop, unhealthy cop — there’s the official delegation, and Abramovich has a little bit extra freedom. He’s one other arm of the Kremlin — not an official arm, however a softer one.”

For Chelsea supporters, particulars of Mr. Abramovich’s function as an obvious middleman has solely led to additional confusion about how the billionaire oligarch ought to be regarded. “The actual fact he’s attempting to dealer peace does put a barely totally different slant on issues than how they seemed to be two or three weeks in the past,” stated Tim Rolls, a member of the Chelsea Supporters Belief. “I feel some assume he’s been exhausting carried out by nevertheless it’s not possible to know what the state of affairs is.”

What shouldn’t be unsure is the admiration for Mr. Abramovich that many Chelsea followers nonetheless have for the person who invested closely of their workforce and took it to new heights.

“I feel it’s not possible for a layman like me to know precisely how shut he’s to Vladimir Putin,” Mr. Rolls stated. “For me and supporters it’s been great. He’s taken us to the subsequent stage, to changing into one of many high six or high eight groups in Europe.”

Tariq Panja and Mark Landler contributed reporting from London, Patrick Kingsley from Tel Aviv, and David D. Kirkpatrick from New York.